In food terms, Punch Down can mean two means.
The first mean involves dough, or more precisely, forcing the air (technically, C02) out of risen dough.
You don’t actually punch the dough — you might hurt your wrist against the work surface. You either press the dough down, or knead it gently several times. The ideal is to fold and press, fold and press, about 20 to 30 times, though some people like to make a great show of it, making a fist and lightly pounding the dough.
Punching the dough down causes the gluten in the dough to relax, and equalizes the temperature of the dough. It also evens out the rising, getting out any large over-sized gas bubbles that may have formed that would cause an uneven crumb in the bread.
After this, the dough is usually shaped for its final rise before baking.
Even bread machines have a punch-down cycle
The second meaning of Punch Down is used in winemaking, where it is also called “Pigeage.”
In making wine, as the must ferments, grape solids rise to the surface, and form a thick cover. In large commercial vats, the cover can be a foot or two thick, and be very hard – this is called a “cap.” The solids need to be put back in contact with the liquid below.
Most industrial wineries use hydraulic punches, but some smaller winemakers including home enthusiasts still punch it down manually.