Definition of nuts
When we talk about nuts in poker, we are talking about the best possible hand at a specific stage. The nuts preflop is AA, but if the flop comes 2-2-5, then the nuts becomes a pair of 2's in hand for a four of a kind. When we have the nuts, we have the best possible hand. Don't confuse the nuts with a nuts draw. If we have A5 in spades on 2-7-9 with 2 spades, we have a nuts draw, but we don't have the nuts.
Origin of the word nuts
Not everyone agrees with the origin of the word "nuts". nuts in English means "nut" but it can also mean "nuts". Legend has it that in the days of the cowboys, during card games, to ensure that a bet was protected, the nuts were unscrewed from the players' vehicles by putting the nuts (nuts) on the table. This meant that the bet was insured and the loser would not be able to run away. Although you can have the nuts at any stage of a hand, the term "nuts" will generally be used for the river only since the nuts at the flop is not necessarily the same as the nuts on the river.