This is 5 cards in a hand that are in ascending order of rank such as 8, 9, 10, Jack, Queen & King.
If 2 players both have a straight they will compare them to see who has the highest ranked hand.
The ‘nut straight’ is the best possible straight as determined by a player’s hole cards as well as the community cards. For example, if the board is 6-7-8-Q-K although several straights are possible on this board, the nut straight is 6-7-8-9-T.
If players have all the cards in their Straight in the same suit, they have a Straight Flush which is worth more.