To call a bet on the final round of betting with a relatively weak holding after suspecting the betting player is bluffing, so described because the call is considered especially “heroic” or brave. For example, in hold’em a board comes , a player makes a large bet, and his opponent calls holding only for a pair of sixes after suspecting his opponent is falsely representing having a flush or an ace. The lead bettor then shows for no pair, and the player making the “hero call” wins the pot.
“Hero call” can also be used to describe a similar call that does not win the pot, too (e.g., if the river bettor in the above example did indeed have a flush or an ace). See “bluff catcher.”