Noun
(mathematics) The difference (sometimes defined to be the absolute difference) between the measured or inferred value of a quantity and its true value.
(military gunnery) Shortest distance between the center of impact or the center of burst of a group of shots, and the point of impact or burst of a single shot within the group.
(military gunnery) Error of a sight consisting of its error in relation to a master service sight with which it is tested, including the known error of the master service sight.
Source: en.wiktionary.org