(scientific computation) An extra option added to a routine without changing the calling sequence. For exAMple, instead of adding an explicit input variable to instruct a routine to give extra diagnostic output, the progrAMmer might just add a test for some otherwise meaningless feature of the existing inputs, such as a negative mass. The use of hidden flags can make a progrAM very hard to debug and understand, but is all too common wherever progrAMs are hacked in a hurry. [Jargon File] (1994-11-24)