What is "hidden" in table tennis?

Hidden, in table tennis, means the act of the paddler serving obstructing the opponent's vision when the ball makes contact with the racket during the serve.

This makes it difficult for the opponent to understand what kind of spin the serving paddler is imparting on the ball, putting him in a disadvantage.

The server can't block the opponent's vision in any manner and the referee rightly caught Manush.