A straight is a hand in poker where the player completes a hand with 5 cards in sequential rank. The suit of the cards, in the case of a straight, does not matter and it is only the rank of the card that makes or breaks the straight. If two or more players make a straight, then the tie is broken by seeing the player with the highest ranked card in the straight.
The straight is always ranked higher than a three of a kind but is ranked below a flush and everything above it. An example of a straight hand would be 5-6-7-8-9 or 10-J-Q-K-A. Ace is the only card that can be used to make the highest straight as well as the lowest straight.
Another usage of straight is when the term is used to indicate the amount that a player is betting into the pot. Instead of claiming the call and the raise amount separately, straight refers to the total amount of the two. For e.g. if player A bets $10 and B raises it by $10, then it can be said that B raises it to $20 straight.