Poker tournaments
Some organizations will allow players to either re-buy or to buy-back, both of which offer players the chance to get more chips if they feel they need them. Sometimes tournaments will only offer re-buy services to players who really need them (in other words they've been on a losing streak), but most of the time any player will be allowed to purchase more chips. Once a player is out of chips and is no longer willing to buy more they are out of the tournament.
Player numbers at each table at poker tournaments is maintained at an even level by constantly moving them around, possibly by swapping one player to a new poker table or breaking up entire tables and distributing their players among other, pre-existing tables. Some tournaments, however, determine ranking by waiting until all other players at a table are eliminated and then moving the remaining player on to the next round.
Prizes for succeeding in the tournament usually come from buy-ins, though funds from outside the players themselves may be introduced as an incentive for more players to join. Some invitation-only poker tournaments, for example, may throw out the buy-in option and fund any prizes and chip pools through sponsorship revenue, possibly receipts from spectators coming in to watch the show. These tournaments are known as freerolls.
The tournament does not end, generally, until all players but one have been eliminated from the tables. Many informal poker tournaments, however, may end by mutual consent between two remaining players.
A tournament may be open or it may be invitational only. For example, the world's most prestigious tournament, The World Series of Poker, is open, though it requires an entrance buy-in of $10,000.