Side pot
A second pot built once a player is all-in for less. They can only win the main pot; everything above their stack plays on without them.
Three players see a flop. One has forty left and shoves; the other two have three hundred each and both call. The forty from each of the three builds the main pot — a hundred and twenty — and that is all the short stack is eligible to win. When the two deep players keep betting on the turn, that money goes into a side pot which only they can win, because the third player has no chips behind to match it.
The rule is simply that you can only win what you could lose. Every player's contribution is capped at their own stack, and each cap creates a new layer. Two short all-ins for different amounts produce two side pots, three produce three, and they are stacked in order — most rooms award the last side pot created first and work back down to the main pot.
At showdown all live hands are shown, including the all-in player's. It is entirely normal for the short stack to win the main pot with the best hand while the two deep players fight over a side pot worth several times more; that is the whole reason the structure exists.
The mistake that costs money is forgetting the side pot exists while it is being built. Two players still with chips behind should almost always check down a hand against a covered all-in — betting into a dry side pot only chases out the player you could have beaten, and lets a third hand survive that would have lost to both of you.
FAQ
What is a side pot in poker?
A separate pot created once a player is all-in for less than the others. Their contribution caps the main pot, and every chip bet beyond that goes into a side pot that only the players with chips behind can win.
Can an all-in player win the side pot?
No. You can only win money you could have lost, so a player who is all-in for less is eligible for the main pot alone. The side pot is contested by the remaining players regardless of who holds the strongest hand overall.
Which pot is paid out first?
The last side pot created is awarded first, then each earlier one in turn, and the main pot last. All live hands are shown at showdown, including the all-in player's, before any pot is pushed.