a very popular type of board game that has been sold since the 1930s. Players use toy money to buy streets and buildings on squares on the board, and then make other players pay rent if they move onto those squares. The squares on the board show the names of real streets in cities in the US (=in an American Monopoly set), London (=in a British Monopoly set), or other big cities around the world. People sometimes use the expression Monopoly money to mean a very large amount of money
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.