unexploded ordnance

The International Mine Action Standards define unexploded ordnance, usually shortened to UXO, as explosive ordnance that has been primed, fuzed, armed or otherwise prepared for use or used. It may have been fired, dropped, launched or projected yet remains unexploded either through malfunction or design or for any other reason.

The definition turns on history rather than purpose. UXO is defined by what happened to it: it was used and it failed. A landmine is the opposite case, an object placed deliberately and working exactly as intended when it explodes. They sit as separate categories under the wider heading of explosive ordnance, which is why clearance operations count and report them separately.

That distinction explains a pattern readers meet in clearance stories, where the number of unexploded items found is far larger than the number of mines. Croatia's clearance, for instance, destroyed nearly 107,000 landmines and about 470,000 items of unexploded ordnance. The two figures are measuring different things, and only the first counts toward a declaration of being mine-free under the Mine Ban Treaty. You may also see the broader phrase explosive remnants of war, which covers unexploded ordnance together with ammunition that was abandoned rather than fired.