The Free On-line Dictionary of Computing (19 January 2023):

Zero and Add Packed

    (ZAP) An IBM 360/370 assembly language	instruction
used when
   performing packed decimal arithmatic to	initialise an accumulator
or to set
   the byte at a given address	to a given value.

   Use of the ZAP instruction is rumoured to be involved in the
SuperZap utility program.

   (2021-03-21)