Definition of stack
A stack is a stack of chips. When we talk about a stack, we mean the number of chips a player has (in tournaments) or the money he has in front of him (in cash games). A typical Hold'em stack is 100 big blinds. 100 big blinds is a standard stack. ?? 200 big blinds and more, you are deepstacked. ?? 30 big blinds and under, you are shotstack. Stack is an important aspect of poker. It is a tool just like your cards in your hand or your bets.
Intimidate with its stack
If you play in tournaments, you know what it's like. If you're at the final table of a tournament and you're the 2nd player in chips, you know that if you play a hand against the chipleader and you're unfortunate enough to be out of position, he could give you a hard time. Against a shortstack, you figure your losses are locked in and even if you lose that 15 or 20 big blinds, you'll stay in the game. But when you have 105 big blinds and you're playing against a player with 150 big blinds, you know the decisions are going to be tougher. With 15 big blinds, you don't have enough ammunition to make a big bluff, but with 150, you do!