To process each element of a list of things."Hold on, I' ve got to loop through my paper mail."Derives from the computer-language notion of an iterative loopcompare "cdr down" (under cdr), which is less common among C and Unix programmers.ITS hackers used to say "IRP over" after an obscure pseudo-op in the MIDAS PDP-10 assembler.[Jargon File]