In some backgammon games, you have a great edge over your opponent, that gives you an opening with which you can win a gammon or backgammon game.
Winning a gammon game occurs, when you have finished bearing off all of your checkers, while your opponent still has not borne off any checkers. This kind of win gives you double the score of the doubling cube.
Winning a backgammon game happens, after you finish bearing off all of your checkers, while your opponent still had one or more checkers in your home board or on the bar, and has not borne off any checkers yet. This means you win three times the value of the doubling cube.
A common example of a gammon game occurs when you have a six prime, and you block one or more of your opponent's checkers behind it. In this case the leading backgammon player needs to ensure that his checkers are not hit upon, and he also needs to remain blocking the opponent as long as possible, so as to ensure he doesn't manage to bear off.

An example of a six prime
There are many types of backgammon positions from which you can win a gammon game. The first example we will discuss occurs when there is a row of white checkers making a five prime in the home board, and two black checkers in the 1 point. Here the white should go for the gammon and continue to block the opponent as long as possible.
When you feel you might lose a gammon game, you can use a few simple techniques, in order to save your game and lose less points.
Felicity Stone - Technical Writer