Paper tape or cards perforated to permit mechanical (electrical or optical) "reading" of the pattern of perforation
s, from which the perforated material (known as chads) has been completely removed. The "chadded tape" method perforated a u-shape which was then fold down (like a pop-top
on beer and soda cans) : no confetti to manage, but the risk
that dangling chads might not stay folded out of the hole and could obscure the perforation, causing a reading error. This risk became famous during the counting of the votes in Florida
(U.S.A.) in the November, 2000 Presidential election
when chad-induced errors reached unaccepted levels in a tight race. The terms "chad" and "chadless" were discovered by the wider public thanks to this event, but had been in use by specialists many years prior.
Reference : "A Dictionary of Computer", Anthony Chandor, Penguin Books, 1973.