A directive used in ibm object code card decks (and later ptf tapes) to REPlace fragments of already assembled or compiled object code prior to link edit. Recompiling or reassembling the source code to produce a whole new object module was only possible if the source code was available, which it rarely was (if you had the object you were lucky!) It was also quicker to apply incremental changes with REP cards and they also circumvented the checksums and card sequence numbers present in the object code.