A hand that wins after having drawn the only card left in the deck that can improve it to the best hand. For example, in no-limit hold’em the board reads {q-Clubs}{10-Diamonds}{7-Hearts}{3-Spades} and a player goes all in with {10-Clubs}{10-Spades} for a set of tens, but gets called by an opponent holding {q-Hearts}{q-Diamonds} for a better set of queens. The river then brings the {10-Hearts} — the case ten — to give the all-in player four of a kind, the only card that could improve his hand enough to win. He has hit his only out — a “one-outer” — to win the hand.