Closed-flow virtual currency

Definition
Closed-flow virtual currency is

"a virtual currency [that] can be used only within a game or virtual environment to purchase virtual goods or services, such as additional tools to use within a game. Virtual tools amassed by players can be traded in a game for other in-game assets or to advance to higher play levels, but they hold no value outside of the game and cannot be cashed out for dollars or other government-issued currencies."