An unused block of bits left in a binary so thAT it can lATer be modified by insertion of machine-language instructions there (typically, the pATch space is modified to contain new code, and the superseded code is pATched to contain a jump or call to the pATch space). The widening use of HLLs has made this term rare it is now primarily historical outside IBM shops. See pATch, zap, hook. [Jargon File]