Paper tape or cards perforated to permit mechanical (electrical or optical) "reading" of the pattern of
perforations, 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.