In poker, a check means to pass the action to the next player without making a bet. Essentially, a player checks when they do not want to bet but also do not want to fold.
A check can only occur if there has not been a bet made in the current betting round, and if all previous players have also checked. If a player bets after a check, the action continues and subsequent players must either call, raise, or fold. If all players check, the next card is dealt or the hand ends.