My opinion
Whenever you look at the board, there will ALWAYS be "The Absolute 2 Best Cards" that someone can hold for the Absolute Best hand FOR THE BOARD. Now that doesnt mean that "the nuts" cant change. Someone defined earlier that AK would be the Nuts if A A K came out... Sorry... AA would be "The Nuts". (Now if you DO have AK, you can still consider yourself as having the nuts because there are only 4 aces and someone else COULDNT have AA because that would mean 5 aces. But AA would still be the better hand) In one of my
poker books, it has exercises that shows you Several flops, and you have to decide What is the Best 3
hands possible. For A A K, The Best Hand would be AA. (Quad Aces) The 2nd best hand would be A K (Aces Full) and the 3rd best hand would be KK (Kings Full).
Here is an example straight out of the book.
Flop:

anyone holding a 2 4 in their hand has the absolute best hand at this point. "The Nuts". But that doesnt mean it wont change. AA would be the 2nd best hand and 55 would be the 3rd best hand.
Turn:

2 4 is no longer "The Nuts" 33 would be "The Nuts" (Quads). AA would still be 2nd best (Aces Full). 55 would be 3rd best (5's full). A3 would be 4th best, 53 would be 5th best and 24 now just dropped to 6th.
River:

Who has the nuts now? I do with

. The only reason why I do is because you felt confident enough with your "Nuts" on the turn (33) and allowed me to out draw you. When playing, you need to determine how many hands out there that CAN beat you with the cards showing and what CAN beat you if other cards come out and bet accordingly.
I just showed you "The Nuts", and "The Nuts" Can and do change on every street of play. Although Holding The

with another diamond... Well, its a good hand... it may be "A Nut Flush"... but not "The Nuts"
My Opinion