The Passive block is a safety and sometimes slow shot that is used to enhance control. It is often used against fast and strong top spins, especially when you don't have too much time to react.
To do a passive block, you only have to hit the ball after it bounces letting your bat hit the ball and keeping it steady. Depending on the speed, spin and arc of your oponnent's shot you will have to adjust the angle of your bat in order to gain control and direct the ball where you want.
These are sub-pages of the Passive block page (a child in the hiararchy).