Originally Posted by Leingod

A souffle is an egg dish that results in overly light and fluffy savory food.

To stiffen peaks means you seperate the yolk from the egg whites. You then whisk the egg whites until your arm falls off. This results in the whites basically forming into a froth that will stand on its own when you lift it up.

A souffle relies on a lot of air incorporated into the egg whites to stay at a respectable height when cooked. The froth and resulting peaks you get from beating the egg whites is the result of this.