To rebuy in poker is to purchase more chips for use at a poker game.
To rebuy in a cash game is to simply purchase more chips. This can only be done when a player is not involved in a current hand (you cannot purchase chips from the time you have been dealt a hand until the time you fold it or muck it).
Generally, players are allowed to purchase as many chips as they would like, subject to house rules and table limits. Some no-limit games have maximum buy-ins, and in those cases, a player is not allowed to purchase a quantity of chips which would put them over that limit.
Most games have table minimums. Rebuys for less than the table minimum are called short buys, and are often subject to restrictions by the casino, and may even not be allowed, depending on house rules.
The term "rebuy" is most commonly used in tournaments, where it has a very specific meaning: in some tournaments, players are allowed to purchase more tournament chips for use in the tournament. Doing so is called a "rebuy". As with cash games, a player cannot rebuy while they are an active player in a hand.
Most tournaments have very specific rules about rebuys, though the rules vary from tournament to tournament. Players should always find out the rules about rebuying when they enter a tournament, as the ability to rebuy can greatly affect a player's tournament strategy.
Sometimes, players are restricted as to the number of rebuys they may make (often only one). Usually, rebuys are only allowed if a player is below a certain level of chips (usually the player must be at or below the starting amount of chips in order to rebuy). Usually, rebuys are also restricted to a certain time period in the tournament (e.g. only during the first three levels, or the first hour of play). Sometimes, players may be allowed to make a "double rebuy" if they have lost all their chips.
There is also a common special type of tournament rebuy called an add-on. Add-ons are distinguished from rebuys in three ways:
- All players are allowed to purchase the add-on, regardless of how many chips they have
- Add-ons are only allowed at one specific moment during the tournament (usually at the first break, which is also when the ability to rebuy is usually suspended).
- Add-ons usually provide more chips for the money than rebuys (e.g. $2000 in tournament chips for $50 cash, instead of just $1000 in tournament chips for $50 cash), due to the fact that they must be done later in the tournament than a typical rebuy, when the blinds have been raised enough that more chips would be necessary.
Players are only allowed to purchase one add-on, regardless of their chip position, though many casinos allow a player to simultaneously purchase rebuys and the add-on at the same time (during the first break), if they are eligible to purchase a rebuy.