patch space n. 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contain new code, and the superseded code is patched to contain a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 (sense 4), zap (sense 4), hook.