What is an illegal hit in volleyball?

A volleyball hit could be legal or illegal hit but it depends on several circumstances. I just want to add up a basic example in my answer: a team can only hit the ball three times before it must go over the net to the opponent's side. A fourth hit is illegal. Well if a block didn’t constitute a hit, in that particular circumstances a team can block up a shot and can continue forward to hit it three more consecutive times.