A side pot in poker is created when there are three or more players in the game, and one of them went all-in during the previous betting rounds, and the remaining players still have some chips to play.
While all of the players still in the hand are playing for the main pot, only those who contribute additional money can win the side pot.
For example, let’s say there are three players in the Texas Hold’em hand. Player A has $100, and players B and C have $200 each. If Player A moves all in and is called by both Player B and Player C, $300 goes to the main pot, and all three players are eligible to win it.
Any additional bets will go to a separate side pot that the all-in player won’t be playing for, so only Players B and C will compete for it. In theory, there could be multiple side pots if there are many players with short stacks.