Proofing a yeast dough means allowing it to rise and double in size before baking. This is typically done by letting the dough rest in a warm and moist environment for a period of time, which allows the yeast to feed on the sugars in the dough and produce carbon dioxide gas. This gas gets trapped in the dough, causing it to expand and rise. Proofing the dough also allows the gluten to relax and become more elastic, which makes the dough easier to shape and results in a lighter, fluffier texture when baked. Therefore, proofing is an important step in the bread-making process that helps to ensure a good rise and a delicious, airy texture in the finished product.