1. An unscrupulous business scheme for making money by dishonest means: The police were able to arrest the gang which was running a scam out of a basement.
2. A situation in which a person has been deprived of something by means of deceit; such as, a confidence game or other fraudulent scheme; especially, for making a quick profit; a swindle: Every day people read in the papers about those who have fallen prey to criminal scams because someone was trying to deceive them in order to get their money.
3. Etymology: from 1963, used as a noun or a verb; U.S. slang; said to be a carnival term, of unknown origin; however, it is obviously related to "fraud" in meaning.