The Free On-line Dictionary of Computing (30 December 2018):

SuperZap

    An IBM utility program used to quickly patch
   operating system or application program executable code
   in preference to editing the source code and recompiling.

   The SuperZAP program was a quick hack written by one IBM
   Engineer, possibly from IBM UK, in the late 1960s to directly
   fix executable files.  He needed to fix a bug but it would
   have taken hours to rebuild the vast OS/360 executables.

   The S/360 architecture has an instruction ZAP (Zero and Add
   Packed) for packed decmial arithmetic, that sets the byte at
   a given address to a given value.  Superzap used this to write
   data given as a string of hex digits to a given location in an
   executable file in a matter of seconds.

   Soon the IBM development labs were releasing all Programming
   Temporary Fixes (PTFs) to OS/360 in this form.  OS/360
   included a version called IMASPZAP or AMASPZAP which persisted
   through MVS, MVS/SP, MVS/XA, OS/390 and probably still
   remains in z/OS, the distant descendent of OS/360.

   [Private 2004-02-05 e-mail from Chris Gage, IBM employee and
   SuperZap user, 1970-].

   (2007-03-15)