1. [common] The perforated edge strips on printer paper, after they have been separated from the printed portion. Also called selvage, perf, and ripoff.
2. The confetti-like paper bits punched out of cards or paper tape; this has also been called chaff, computer confetti, and keypunch droppings. It's reported that this was very old Army slang (associated with teletypewriters before the computer era), and has been occasionally sighted in directions for punched-card vote tabulators long after it passed out of live use among computer programmers in the late 1970s. This sense of ‘chad’ returned to the mainstream during the finale of the hotly disputed U.S. presidential election in 2000 via stories about the Florida vote recounts. Note however that in the revived mainstream usage chad is not a mass noun and ‘a chad’ is a single piece of the stuff.
There is an urban legend that chad (sense 2) derives from the Chadless keypunch (named for its inventor), which cut little u-shaped tabs in the card to make a hole when the tab folded back, rather than punching out a circle/rectangle; it was clear that if the Chadless keypunch didn't make them, then the stuff that other keypunches made had to be ‘chad’. However, serious attempts to track down “Chadless” as a personal name or U.S. trademark have failed, casting doubt on this etymology — and the U.S. Patent Classification System uses “chadless” (small c) as an adjective, suggesting that “chadless” derives from “chad” and not the other way around. There is another legend that the word was originally acronymic, standing for “Card Hole Aggregate Debris”, but this has all the earmarks of a backronym. It has also been noted that the word “chad” is Scots dialect for gravel, but nobody has proposed any plausible reason that card chaff should be thought of as gravel. None of these etymologies is really plausible.