The nuts is a common poker term for the best possible hand. The term has particular significance in variants of poker that use community (board) cards, such as Hold 'em and Omaha, since the possible number of hands a player can have is limited, and it's usually easy to determine what the best possible hand would be based on the board. In draw games, where all cards are concealed, the nuts is static: For example, in five-card draw for high, a royal flush is always the nuts; in deuce to seven lowball games, such as deuce to seven triple draw, 75432 without a flush (a "wheel") is always the nuts, unless you know from discards that a wheel is not possible in your opponent's hand.
Note that the nuts is not the best hand that a player actually has, but is instead the best possible hand. It frequently occurs that no player actually has the nuts.
Learning to recognize the nuts for a given board is an important skill in poker; top players can name the nuts for a board instantly.
The lowest possible nut hand on a complete Texas hold 'em board is three queens, this being the nuts when the board reads Q-8-7-3-2 without three or more cards of the same suit. Lower sets can never be the nuts because straights are always possible if jack or less is the highest card on any complete board of unpaired cards. Three sevens can theoretically be the nuts after the flop, three eights can be the nuts after the turn.
The nuts is the best possible hand given the current board of community cards, even if the board is not yet complete. It is possible, and indeed not uncommon, for a player to flop the nuts, and then have their hand beaten on the turn as another player makes the nuts on the turn.
Frequently, the best possible hand on the flop is not the same as the best possible hand on the turn, or the best possible hand on the river. A common complaint among unlucky players is that they "flop the nuts, and keep getting rivered." This is certainly possible when the flopped nuts are a straight or a set, since both hands are easily beaten by flushes or full houses if the board brings up three of a suit or shows a pair.
The second-best possible hand for a given board is called the second nuts. The third-best possible hand is called the third nuts, and so on.
Unskilled or imprecise players sometimes refer to the best hand in play as the "nuts" (as in, "I had the nuts all along, guy!"), but this is incorrect and will quite often cause another player to correct the speaker. Sometimes, however, this is used sarcastically or ironically: after an entire hand is checked to the river and the winner turns over his pocket deuces, he might exclaim "I should have been betting this monster - I had the nuts!".
Origin of the term
The origin of the term "nuts" is in some dispute, since it has been in use since before poker lingo was recorded, but the most common story is that it comes from the American Old West. Apparently, if a poor farmer ran low on money, he would go out to the stable where his horse and wagon were hitched, unscrew the nuts from the wheels (making it impossible to ride away on the wagon), and return to his poker game. He would then proceed to "bet the nuts" only when he had the best possible hand, and the phrase gradually came to mean betting on the best possible hand, and then it came to describe the best possible hand itself.