There is a wide misconception that the Push is actually a topspin block. A push is actually an underspin stroke played over the table. It is like a mini chop. When an underspin stroke is played further from the table, it is a "chop". When an underspin stroke is done over the table it is a "push".
The push is a very important part of the short game because it generates a spinny ball that is hard to attack. The opponent may be able to loop it but it won't be particularly dangerous. A bad return from your opponent can open up the chance to attack.
These are sub-pages of the Push page (a child in the hiararchy).