To call means putting in the same amount as the latest bet to stay in the hand. It differs from raising, which increases the bet, and from folding, which gives up the hand and any money already in the pot. Whether a call makes sense depends on the pot size, the cost of the call and the chance of winning, which players compare using pot odds. Calling is also used in other games, such as when a player says call to match a bet in a betting round.
Example
The pot holds 30 units and an opponent bets 10. Calling costs 10 to try to win a pot of 40, so the call needs a better than 1 in 5 chance of winning to break even.