Copying credit or debit card data (account numbers, PINs, expiration dates) during legitimate transactions in order to make unlawful ones later. In a restaurant, when waiters take the customer's card away to authorize the transaction, it is very easy to jot down the number or run the card through a reader.
Skimming devices can be placed over card readers at ATMs and gas pump terminals. Casual users may not notice that the reader has an unusual shape or is larger than normal, which indicates a skimmer is being used. See EMV
In Europe, wireless mobile terminals are widely used to authorize the card in front of the customer. However, they are not found in the U.S. because the machines are generally not set up for signatures. In addition, American diners may feel intimidated telling the waiter how much of a tip to include.