When a poker room hosts a tournament for which they have set a guarantee on the prize pool and not enough players participate to meet that prescribed amount, the room will add the needed money to meet the guarantee, with that addition referred to an an “overlay.”

For example, say a tournament has a $100+$20 buy-in — meaning $100 of each player’s entry goes to the prize pool and $20 is for tourney fees — and that tournament is advertised as having a $10,000 guarantee. That means at least 100 players need to enter the event for the prize pool to reach $10,000. However, if only 80 players participate, that means players will have only contributed $8,000 to the prize pool, and so the poker room will have to supply the other $2,000 to meet the guarantee. The event will then be said to have had an “overlay of $2,000.”