Skimmer
Skimmers are essentially malicious card readers attached to real payment terminals so that they can harvest data from every person that swipes their cards. The typical ATM skimmer is a small device that fits over an existing card reader.
Skimming
Skimming is considered a type of white-collar crime,and is described as the theft of cash from a business prior to its entry into the accounting system for that company. Although skimming is one of the smallest frauds that can occur, it is also the most difficult to detect.
Skimming cash receipts
Skimming is slang for taking cash "off the top" of the daily receipts of a business (or from any cash transaction involving a third interested party) and officially reporting a lower total. The formal legal term is defalcation. Even though skimming is one of the smallest frauds that could appear, they are considered as the most difficult fraud to detect.