Glossary

Plain-language definitions of the technical terms in our reporting. Every entry is checked against a source, the same as every story.

Climate & Energy

Legal Amazon An administrative region of Brazil covering nine states and about 59 percent of the country, which is not the same thing as the Amazon rainforest.
PM2.5 Airborne particles about 2.5 micrometres across or smaller, fine enough to be drawn deep into the lungs, and the form of air pollution linked to the most early deaths.
PRODES Brazil's official satellite programme for measuring annual deforestation, whose reporting year runs from August to July rather than matching the calendar.
capacity factor The share of its maximum possible output a power plant actually delivers over a period, comparing electricity produced with what running at full power throughout would have produced.
carbon dioxide equivalent A common unit for greenhouse gases: each gas is converted into the amount of carbon dioxide that would cause the same warming over 100 years.
installed capacity The maximum power a generator or a whole fleet could deliver at once if everything ran flat out, set by the equipment rather than by how much it actually runs.
ozone hole Not a gap with no ozone in it, but a region over Antarctica where ozone thins below a defined threshold each southern spring.
ozone-depleting substance The family of nearly 100 manufactured chemicals controlled by the Montreal Protocol because they destroy ozone in the stratosphere.
perovskite-on-silicon tandem cell A solar cell that stacks a perovskite layer on a silicon one so each captures a different part of the spectrum, beating the ceiling for any single layer.
solar cell efficiency The share of the sunlight falling on a solar cell that it converts into electricity, a figure with a hard theoretical ceiling for any single-layer cell.
storage duration How long a battery can keep delivering electricity at its full rated power before it is empty, found by dividing the energy it holds by the power it can release.
terawatt hour A unit of energy equal to a trillion watt hours, used for the electricity a country or a continent generates over a period.
territorial emissions Greenhouse gas emissions that physically occur inside a country's borders, the basis used for national targets and United Nations reporting.

Health & Medicine

HPV Human papillomavirus, a very common sexually transmitted infection that usually clears by itself, but whose high-risk types cause almost all cervical cancer.
JAK inhibitor A drug that blocks Janus kinase enzymes, which relay the signals driving the body's immune and inflammatory responses, so inflammation is turned down.
LDL cholesterol Low-density lipoprotein cholesterol, often called the harmful cholesterol, is the form that collects in artery walls; high levels raise the risk of heart attacks and strokes.
One Health An approach that treats the health of people, animals, plants and ecosystems as one connected system rather than four separate problems.
PCSK9 inhibitor A PCSK9 inhibitor is a medicine that blocks the PCSK9 protein so the liver can clear more LDL cholesterol from the blood, producing large drops in cholesterol levels.
RAS A family of genes, and the proteins they make, that act as on/off switches for cell growth; mutated versions jam in the on position and drive about a third of human cancers.
Subgroup analysis A look at how a treatment worked in one slice of a trial's patients rather than all of them, which carries less weight than the trial's main result.
Unsafe abortion WHO's term for an abortion carried out by someone without the necessary skills, or in a setting below minimal medical standards, or both. It describes conditions, not legality.
WHO Framework Convention on Tobacco Control The first global public health treaty, adopted by the World Health Assembly in 2003 to tackle the causes of the tobacco epidemic that cross national borders.
Wolbachia A bacterium that lives inside the cells of many insects and, when put into mosquitoes, cuts their ability to pass on dengue and related viruses.
accelerated approval A US licence granted on a measurement thought to predict a real benefit, rather than on the benefit itself, on condition that a later trial confirms it.
adverse event Any unfavourable change in a trial participant's health recorded during the study, whether or not the treatment caused it.
amyloid plaque A clump of a protein called beta-amyloid that builds up between nerve cells in the brain; plaques are a hallmark of Alzheimer's disease.
antimicrobial resistance When bacteria, viruses, fungi or parasites stop responding to the medicines meant to kill them, so infections that were once routine to treat become hard or impossible to cure.
blinding Keeping the people in a trial, and often those treating them and those judging the results, unaware of which treatment each patient received, so knowledge cannot colour what is recorded.
boxed warning The warning the US Food and Drug Administration requires to be printed inside a box at the top of a drug label, reserved for risks that may lead to death or serious injury.
bronchiolitis A common viral chest infection in babies that swells the smallest airways in the lungs, making breathing and feeding hard work.
cataplexy A sudden episode of muscle weakness, usually triggered by strong emotion such as laughter, during which the person stays fully conscious throughout.
cohort A group who share a defining trait, often the year they were born or treated, and who are then followed together over time.
community health worker A health worker who lives in the community they serve and is trained for less time than a nurse or doctor, delivering basic preventive and curative care outside a clinic.
concentration-response function An equation, built from epidemiological studies, estimating how much the risk of a given health outcome rises for each extra unit of a pollutant in the air.
controlled substance schedule One of five US categories, set by the Drug Enforcement Administration, ranking a drug by its accepted medical use and its potential for abuse and dependence.
dermatomyositis A rare autoimmune disease in which the immune system attacks a person's own muscles and skin, causing progressive muscle weakness and distinctive rashes.
disability-free survival A trial measure of healthy life span: the time a participant stays alive, free of dementia and free of lasting physical disability, counted as one combined outcome.
dopamine agonist A Parkinson's drug that imitates dopamine rather than replacing it, attaching to the receptors on brain cells that dopamine normally uses and switching them on.
double reading The European standard for checking screening mammograms: two readers examine the same images independently, with a consensus discussion or a third opinion settling any disagreement.
dyskinesia Unwanted, involuntary movements such as twisting and writhing, which in Parkinson's disease can be a side effect of the medicines that treat it.
elimination as a public health problem A formal WHO status meaning a disease has been pushed below an agreed threshold in a country, which is not the same as wiping it out.
endpoint The precisely defined measurement a trial analyses to answer a question. The primary endpoint is the trial's main question; secondary endpoints are the ones asked alongside it.
evaluable In a clinical trial, a participant whose data could actually be assessed for the result being measured, often fewer than the number enrolled.
event-free survival The time after treatment ends that a patient stays free of the setbacks it was meant to prevent, such as the cancer returning or growing.
gene therapy A technique that treats or cures disease by modifying a person's genes, rather than by giving a drug that acts on the body's chemistry.
hazard ratio A measure of how often an event happens in one trial group compared with another over time; below one means the treated group did better, one means no difference.
hierarchical testing An order fixed before a trial's results are analysed, setting which of its main questions is tested first and stopping confirmatory claims once one of them fails.
immunotherapy Treatment that uses substances to stimulate or suppress the immune system so that the body can fight cancer, infection and other diseases.
incidence rate How often new cases of a disease appear in a population over a set time, usually given as new cases per 100,000 people per year.
interval cancer A cancer diagnosed in the gap between one screening round and the next, after a screening test that did not detect it. Programmes count them to measure what the screen missed.
lifetime risk of maternal death The chance that a 15-year-old girl will eventually die from a maternal cause, if today's birth rates and death rates hold and other causes of death are allowed for.
maternal death The death of a woman while pregnant or within 42 days of the pregnancy ending, from a cause related to or made worse by the pregnancy, but not from an accidental one.
maternal immunisation Vaccinating a pregnant woman so that the antibodies she makes cross the placenta and protect her baby in the first months of life, before the baby can be vaccinated.
maternal mortality ratio The number of maternal deaths in a period for every 100,000 live births in the same period, the standard measure of the risk childbirth carries for the mother.
messenger RNA A single-stranded molecule that carries the instructions for building one protein from a cell's DNA to the machinery that assembles the protein.
neglected tropical disease A WHO category for a diverse group of diseases, caused by many different pathogens, that mainly affect the poorest communities.
non-inferiority A trial result showing that a new treatment is not materially worse than an existing one, measured against a margin fixed before the trial begins, rather than that it works better.
off time In Parkinson's disease, the hours of the day when a dose of medicine has worn off and the slowness, stiffness or other symptoms return, usually between doses.
open-label trial A study in which both the patients and the people treating them know which drug or treatment is being given.
opioid A class of drugs that act on the brain's opioid receptors, covering compounds extracted from the poppy plant and the semisynthetic and synthetic ones made to work the same way.
orexin A brain chemical, also called hypocretin, made by a small group of cells in the hypothalamus, that holds the body in a waking state and controls the timing of REM sleep.
pathological complete response No sign of cancer left in the tissue removed at surgery or biopsy after treatment, as judged by a pathologist under a microscope.
post-exposure prophylaxis The emergency course given after a possible rabies exposure: washing the wound, a full course of rabies vaccine, and antibodies into the wound where needed.
prevalence The share of a population that has a given characteristic, such as a disease or a habit, at a given time, usually reported as a percentage.
primary prevention Treating someone who has never had a heart attack or stroke in order to prevent the first one, as opposed to secondary prevention, which protects a patient who has already had one.
progression-free survival The length of time during and after treatment that a patient lives with a disease without it getting worse; a common trial measure, often shortened to PFS.
provisional counts Early death counts published before the records are complete, in two forms: reported counts of what has arrived, and predicted counts adjusted for what has not.
rabies variant A lineage of the rabies virus kept in circulation by one particular group of animals, so a country can clear the dog-maintained lineage while the virus persists in wildlife.
randomised controlled trial A study that divides participants between the treatment and the comparison group by chance, so the groups are alike and the treatment can be judged fairly.
relative reduction A fall measured against the starting level rather than in percentage points: a rate falling from 10 percent to 7 percent is a 30 percent relative reduction.
relative survival The share of people with a cancer who survive it, measured against how long similar people without that cancer would have lived, so that deaths from other causes do not count against it.
retina The light-sensitive layer of tissue at the back of the eye, which turns light into the electrical signals the brain reads as an image.
sensitivity For a medical test, the share of the people who genuinely have the disease that the test correctly identifies. No test reaches 100 percent, because some cases are always missed.
sentinel surveillance Disease monitoring where a small chosen network of clinics or hospitals reports in detail, instead of every site in the country reporting a little.
serious adverse event An adverse event that kills a participant, threatens their life, puts them in hospital, leaves lasting incapacity or causes a birth defect.
single-arm trial A trial in which everyone receives the treatment and there is no comparison group enrolled alongside them, so results are judged against outside data.
specificity For a medical test, the share of the people without the disease that the test correctly clears. No test reaches 100 percent, because some healthy people always test positive.
statin Statins are a widely used class of medicines that lower LDL cholesterol by slowing the liver's own production of it, cutting the risk of heart attacks and strokes.
synthetic opioid An opioid made entirely in a laboratory rather than derived from the opium poppy. Fentanyl is the one that dominates overdose deaths.
trichiasis Eyelashes that turn inward and rub against the eyeball; when repeated trachoma infection scars the eyelid into that position it is called trachomatous trichiasis.
vaccine effectiveness How well a vaccine works once it is rolled out to a real population, as opposed to how well it performed inside the trial that licensed it.
vaccine efficacy The percentage by which a vaccine lowered the risk of disease in a clinical trial, measured against whatever the comparison group received.
years of life lost A measure of early death counting the years people would statistically have lived had they not died young, rather than counting the deaths themselves.

Nature & Conservation

Green Status of Species The IUCN's companion assessment to the Red List, scoring from 0 to 100 percent how far a species has recovered towards its full range and function.
IUCN Red List The IUCN's ranked system for classifying how close a species is to global extinction, from Least Concern up to Extinct.
Unusual Mortality Event A formal US finding that a marine mammal population is dying off unexpectedly and in significant numbers, which triggers an official investigation and response.
calving interval The time between one birth and the next for the same female whale, a measure scientists use to judge how healthy the breeding females are.
capture-recapture A method of estimating how many animals live in an area by identifying individuals, then seeing how often the same ones turn up again.
downlisting Moving a species to a lower-risk category on the IUCN Red List after a reassessment finds its extinction risk has genuinely fallen.
escapement The number of adult salmon that survive the fisheries and reach a river or hatchery to spawn, counted each year as the measure of a run's health.
high seas The parts of the sea that lie outside every country's coastal waters and belong to no state, covering about two thirds of the ocean's surface.
masting Masting is when a population of plants produces seed or fruit in big, synchronised bursts in some years and very little in the years between.
mature individuals The IUCN's count of the animals in a population known or thought to be capable of breeding, which is usually well below the total number counted.
overfished A formal status meaning a fish stock has fallen below a set population threshold. It does not mean too much fishing is happening now, which is called overfishing.
satellite population A group of animals of a protected species living outside the reserve set aside for it, formed as the core population grows and disperses beyond the boundary.
umbrella species A species whose protection shelters many others, because saving it means protecting the large habitat that all of them share.

Science & Discovery

CRISPR A technology that lets researchers change the DNA of a living organism at a chosen spot, adapted from a defence system found in bacteria.
Denisovan An archaic human population identified in 2010 from ancient DNA at Denisova Cave in Siberia, distinct from Neanderthals but sharing ancestors with them.
Hominin The human evolutionary group: modern humans together with their extinct fossil relatives, a rank sitting between genus and family in biological classification.
Mitochondrial DNA The small circular chromosome carried inside mitochondria, the cell's energy compartments, and inherited only from the mother rather than from both parents.
confidence interval The range of values a study reports as likely to contain the true figure, given the data it collected. A wider range means less certainty.
fault-tolerant Describes a quantum computer that keeps computing correctly even though its parts keep making errors, because it detects and corrects them as it goes.
interrupted time series A study design that measures the trend running before an intervention, then measures how far the data after it departs from that trend.
logical qubit A single unit of quantum information spread across many physical qubits, so that errors in any one of them can be spotted and fixed without losing the information.
megajoule A million joules, the joule being the standard unit of energy, used for the energy in a single burst such as a fusion shot.
near-Earth object An asteroid or comet whose orbit brings it within 1.3 astronomical units of the Sun, close enough to pass through Earth's neighbourhood.
neurotransmitter A chemical messenger that one nerve cell releases to carry a signal across the gap to the next cell, where it attaches to a receptor and changes what that cell does.
p-value The probability of seeing a difference at least as large as the one measured if the treatment being tested had no real effect, so a small p-value makes chance an unlikely explanation.
peer review The process of asking independent experts in the same field to assess a scientific manuscript before a journal publishes it.
physical qubit One real piece of quantum hardware, such as a single trapped ion or a superconducting circuit, holding one qubit of information and carrying its own error rate.
quantum error correction The method of spreading one unit of quantum information across many physical qubits and checking them repeatedly, so errors can be found and fixed while a computation runs.
qubit The basic unit of information in a quantum computer, able to hold a coherent blend of 0 and 1 at the same time rather than only one or the other.
reuptake The step in which a nerve cell pulls a chemical messenger it has just released back inside itself, ending the signal. Drugs that block it leave more of the messenger available.
species description The formal published scientific account that names a new species and states in words the features said to set it apart from every other species.
statistical significance The judgement that a difference this large would be unlikely to arise by chance alone, measured against a threshold, usually 5 percent, fixed before the data are analysed.
target gain In fusion, the energy a reaction releases divided by the laser energy delivered to the fuel, which is a much narrower comparison than energy in versus energy out.
tracklet A set of observations of the same moving object taken during one night, linked together as the unit astronomers submit when they report a possible asteroid or comet.
trans-Neptunian object An icy body orbiting the Sun beyond Neptune, in the region that starts about 30 times further from the Sun than the Earth is.

Society & Justice

Basic drinking water service The WHO and UNICEF standard for counting a household as having drinking water: an improved source, within a round trip of 30 minutes or less including queuing.
Mine Ban Treaty The 1997 convention banning anti-personnel mines, which obliges countries to destroy stockpiles, clear mined areas to a deadline and report on progress.
Supplemental Poverty Measure A second US poverty rate that counts taxes, tax credits and in-kind benefits, subtracts work and medical costs, and adjusts its income lines for local housing costs.
World Bank income classification The World Bank's grouping of every economy into low, lower-middle, upper-middle or high income, set each 1 July by national income per person and revised as countries cross fixed thresholds.
anti-personnel mine A mine designed to go off when a person is near it or touches it, which is the specific weapon the Mine Ban Treaty prohibits.
child labour Work that is too young, too long or too dangerous for a child's age, as defined by international labour standards. Light chores and family help that harm neither health nor schooling fall outside it.
child marriage A formal marriage or informal union in which a girl or boy lives with a partner as if married before the age of 18.
conditional cash transfer A payment made to poor households on condition that they take specified actions, usually keeping children in school and using basic health care.
cost of a healthy diet A United Nations measure of what it costs one person a day to buy the cheapest local foods that together meet dietary guidelines, rather than the price of a typical shop.
food insecurity Lacking regular access to enough safe and nutritious food for normal growth and development and an active, healthy life. It is measured by asking people about going without.
hazardous work Work likely to harm a child's health, safety or morals, by its nature or by the conditions it is done in. International standards prohibit it for everyone under 18.
open defecation Disposing of human faeces in fields, forests, bushes, open water, beaches or other open places, or with solid waste. It is the bottom rung of the UN's sanitation ladder.
poverty threshold The income line a statistics agency uses to decide who counts as poor: a household whose income falls below the line for its size and make-up is counted as living in poverty.
purchasing power parity A currency conversion rate that equalises what money buys in different countries by stripping out differences in price levels, so costs and incomes can be compared fairly.
ratification The formal act by which a state consents to be bound by a treaty. Signing a treaty of this kind keeps a state in the process but does not create the obligation.
safe system approach A way of designing roads, vehicles and speed limits on the assumption that people will make mistakes, so that the forces in a crash stay within what a human body can survive.
safely managed sanitation A toilet a household does not share with anyone else, where the waste is either treated safely where it falls or removed and treated somewhere else.
undernourishment Consuming too little dietary energy to maintain a normal, active, healthy life. It is how the United Nations defines hunger when it counts how many people are hungry.
unexploded ordnance Ammunition that was fired, dropped or launched but failed to go off, which makes it a different hazard from a landmine that was deliberately laid.

Technology & Solutions

levels of driving automation A six-step scale, from Level 0 to Level 5, that sets out how much of the driving a car's automation does and whether a human must stay ready to take over.
lithium iron phosphate A lithium battery chemistry whose positive electrode uses iron and phosphate instead of nickel and cobalt, making cells cheaper and longer lasting but heavier for the energy they hold.
photovoltaic Turning light directly into electricity in a material, with no moving parts and no heat engine in between.
trapped-ion A way of building a quantum computer in which single electrically charged atoms are held in place by electromagnetic fields and used as qubits.