What does it mean to proof dough?
Proofing is the formal name for the process that happens when you let dough rise.
During proofing (or proving), yeast leavens the dough when fermentation produces carbon dioxide gas that puffs it up. Dough should be proofed in a warm place without draughts and covered with a clean kitchen towel to prevent a crust from forming.
Depending on the recipe, dough may be proofed once or more.