Basically, a competition game between a group of players over a period of time. For example, in Poker tournaments a bunch of poker players sit down with the same number of chips, and eventually only one player has any chips left. In order to ensure that the event will finish in reasonable time, tournaments institute a schedule by which the blinds and/or antes increase. Tournaments are usually played with chips that have no value outside of the tournament. So a buy-in of $30 might get you $500 in tournament chips to play with, but you can't cash them out in the middle. The winner of a tournament (the last player to bust out) as well as several of the other top finishers are typically awarded prize money according to some predetermined schedule. Tournament details vary widely, but a typical arrangement might include an initial buy-in, a re-buy period during which a player who runs out of tournament chips may buy more, and an opportunity to add on to one's stack after the re-buys have ended. Other details about the structure can vary widely.

This definition is in context to Online Casino. See more contextual defintions for Tournament.