In poker tournament  players  play poker games. In ”heads-up” tournament  few as two players plays on a  table and as many as  thousands of players play on hundreds of tables. Winner is the guy who wins every chip on the table  and the others are awarded places based on the time . To facilitate this, in most tournaments, blinds rise over the duration of the tournament. Unlike in a ring game (or cash game), a player’s chips in a tournament cannot be cashed out for money and serve only to determine the player’s placing.

To enter a typical tournament, a player pays a fixed buy-in and at the start of play is given a certain quantity of tournament poker chips. Commercial venues may also charge a separate fee, or withhold a small portion of the buy-in, as the cost of running the event. Tournament chips have only notional value; they have no cash value, and only the tournament chips, not cash, may be used during play. Typically, the amount of each entrant’s starting tournament chips is an integer multiple of the buy-in. Some tournaments offer the option of a re-buy or buy-back; this gives players the option of purchasing more chips. In some cases, re-buys are conditional (for example, offered only to players low on or out of chips) but in others they are available to all players (called add-ons). When a player has no chips remaining (and has exhausted or declined all re-buy options, if any are available) he or she is eliminated from the tournament.

source en.wikipedia.org