After proving dough, it is "knocked back" or "punched down" to deflate it, releasing trapped air from the fermentation during proving. The words "punched down" are a little misleading - you only need to press down with your fist gently. Knocking back the dough removes larger air bubbles, further improving the texture of the baked bread and making it more uniform. Knocking back also additionally supports the fermentation of the yeast.