(card skim’ming) (n.) The act of using a skimmer to illegally collect data from the magnetic stripe of a credit, debit or ATM card. This information, copied onto another blank card’s magnetic stripe, is then used by an identity thief to make purchases or withdraw cash in the name of the actual account holder.
Skimming works by replacing a card reader like an ATM with a camouflaged counterfeit card reader. The counterfeit reader records all of the data on a credit, debit or ATM card as it passes through the skimmer. In addition to ATMs, other locations where card skimming happens include restaurants, taxis or other businesses where an employee will take the card from the actual account holder in order to run the charge. In these instances, the thief has fitted the card reader with a skimmer, or uses a hand-held skimmer hidden in a pocket.
Also see “How to Protect Against Card Skimming” in the Did You Know…? section of Webopedia.