French meringue
French meringue is the simplest type: raw whites whipped with sugar added gradually. Nothing is heated, so the mass stays raw and needs cooking afterwards.
The sugar does not all go in at once: the whites are first whipped to a light foam, then the sugar is rained in. Added at the start it makes the whites slower and harder to whip, because sugar binds water and weighs the foam down.
French meringue is the least stable of the three and starts weeping if left standing. It is used where the mass goes straight to work: baked-out meringue shells, the base of sponges, the aerating component of mousses, and the classic French macaron method.