Definition of stop and go
A stop and go is a game that a player plays in a sit and go or tournament. The purpose of a stop and go is to maximize folding equity when you are shortstacked. For example, a player has 11 big blinds and is on the big blind. The player in button position makes a preflop raise to 3 big blinds. Rather than pushing all in preflop to 11 big blinds and having limited folding equity, the player who makes a stop and go will call the preflop bet and push all in on any flop.
Why is stop and go effective?
The majority of the time in poker, you miss the flops. With two cards that are not a pair, you hit the flop 1 out of 3 times. So, the stop-and-go player knows that the majority of the time, his opponent will have to fold. And often, the stop-and-go player will make the opponent fold a better hand. Imagine you have JT. The player in button position opens with a pair of 2's. You call the bet and push all in on the flop to A7Q. The player with a pair of 2s will not be able to call the bet. The player with JT will then have folded a better hand.