A pancake block is when a blocker knocks his man down into the ground, aka flat as a pancake.
Four stats come out of this: Pancakes - when you block someone to the ground. Good! Pancaked - when you were blocked into the ground. Bad! Reverse pancakes - when you knock you blocker into the ground. Good! Reverse pancaked - when your blocker knocked you into the ground. Bad!
Just to clear up any future confusion, defensive linemen do not pancake. They GET pancaked. What they do is reverse pancake, also stylized as revcake or simply rcake.