A 'Main Pot' in a hand of Poker

Main pot is the term used when a player is all in and has less than other players at the table, who are still in the hand. The rule of thumb is that you can only win from another player the amount you invest into the pot. Where players who have more chips than you continue to play and bet in the hand, they then play for a side pot. For instance, you are in a three way pot. You have $100 left in your stack and the other two players have $300 and $500 respectively. You hold big slick and decide this is your moment, you push all your remaining chips into the pot.

You get a call by both players and there is now over $300 in the pot. This is known as the main pot. As you have put the last of your money in the pot, you can have no more involvement and can not win more than you have staked. As you bet $100 and were called by 2 other players - the most you can win is the $300 (as well as any antes). Let's now assume that the second player bet's another $100 and is called by player 3. The side pot now has $200 in it. You can't win this.

It is quite possible for two or more different players to go all in at different stages of the hand which could result in multiple side pots being created. The key is that the player that's all-in, can't win anything in the side pot, as they haven't contributed to it.