n (engineering) A representative specimen, taken from the centre a spread of production - a sample with bogey (typical) characteristics.
n (engineering) a standard of performance set up as a mark to be aimed at in competition.
n (context|military|_|slang) An unidentified aircraft, especially as observed as a spot on a radar screen, and often suspected to be hostile. (Also sometimes used as a synonym for bandit - an enemy aircraft)