Definition of fold
The word fold literally means "to fall back". To fold as in "to retreat". We fold our troops and abandon the war. In French, we use the English word fold or "se coucher", which is the action of abandoning a hand. Folding means throwing away your cards, not calling the bet and giving up the main pot. Folding saves us from having to pay a bet, but eliminates us from the hand. If a player folds at any point in the hand, he loses all rights to the prize pool, even if he folds on the river after putting a lot of money into the prize pool.
Knowing when to fold your hand
The fold is one of the most important games in poker. It is probably the most unpleasant play to make, but it is one that you will make with great frequency. Knowing when to bluff is a skill. Knowing when to call a bet is a skill. But knowing when to fold your hand is an even greater skill. The action of folding is probably the most important action you do at the poker table. You have to know when to fold at the right frequency, without being taken advantage of. As they say, a dollar saved is a dollar earned.