Proofing

Proofing, also known as fermentation, is the process of allowing yeast to convert the sugars in dough into carbon dioxide and alcohol. This process causes the dough to rise and develop flavor. In baking, proofing is the final rising stage of dough before baking. Bakers will often proof dough in a warm, moist environment, which allows the yeast to thrive and produce carbon dioxide more quickly. The dough is considered fully proofed when it has doubled in size and has a uniform, spongy texture.

It's also used to refer to the process of activating yeast in order to confirm that the yeast is still viable before adding it to a dough. This is done by dissolving the yeast in warm water with a small amount of sugar and monitoring to see if the mixture becomes frothy, which indicates that the yeast is still active.