In volleyball, a pancake is when the ball is about to hit the floor, and a player desperately dives and slides his/her hand across the floor, in an attempt to cause the ball to bounce off of the back of the player's hand rather than the floor. If executed properly, the ball will bounce back up into the air, allowing another player to pass the ball over the net.
They would have lost the game because of John's bad pass, but Mike desperately performed a pancake, allowing Joe to hit the ballover the net, saving the point.
Mary's pancake was ineffective, because her hand was not directly under the ball when it fell.
During sexual intercourse, the person on top does nothing to support their weight, hence "pancaking" out on their partner. Opposite of starfish. Usually done with dead eyes and zero effort.