Nut

Nut is an adjective in poker (derived from the term nuts) used to describe hands, and means "the best possible" of the hand being described. For example, an ace-high flush is often called the nut flush.

In Hold 'em and Omaha, it is often also used to describe the best possible of the hands which could be made by a player given the current board. For example, the "nut straight" is not necessarily an ace-high straight in hold 'em: if the board is

then the nut straight with this board would be a hand of J-8 (any suits):

because 7-8-9-10-J is the best possible straight that can be made using this board and a player's two hole cards.

As an adjective, nut is most commonly applied to a flush, often when discussing a draw. The "nut flush draw" means the player must catch one more card of the suit they need in order to have the highest possible flush. Usually this means the player holds the ace of that suit (though it can mean the player holding the king, if the ace is already on the board).

It is also very commonly applied to a low in a hi-lo split game: players will often speak of making the "nut low", or of drawing to it.

"Nut" is frequently applied to "straight" as well, as described in the example above, and occasionally applied to a "full house". As an adjective, "nut" is not applied to other hands (pairs, three-of-a-kinds, or quads). The best pair, two pairs, or three-of-a-kind is described as being the "top" (e.g. "top pair", "top two pair", or "top set"), and "nut" is not used in such situations.

More colorful characters have been known to refer to "nut no pair" to mean the best possible hand that has no pair.

Can "nut" be used to describe a non-best hand?
While "nut" by definition means the best of the hands being described, there is some argument over whether it can be applied to a hand if that hand is not itself the best possible of all hands. For example, if the board above had the three of diamonds instead of the three of clubs:

then while a player's J-8 hole cards would still give them the best possible straight, it is no longer the best possible hand, since a flush is now possible.

It's generally agreed that a J-8 hand is not the nuts on this board, since nuts always means the absolute best of all possible hands, but is it even correct to say that a J-8 is the nut straight on this board? A majority of players seem to fall into the "yes, it still has meaning" camp, which implies that "nut" as an adjective means the equivalent of "best": having the "nut straight" is the same as saying the "best straight", which is true, even if it's not the best possible hand. Some players, however, feel that "nut" relates more closely to "nuts" and should only be used to describe the best possible hand.