What Does Reversible And Irreversible Mean?

Well, to be honest reversible means you can change something back, like when you scrunch a paper - you can still open it. But if you rip it in small pieces, then you can't get it back, so that would be irreversible. 

In this picture, the growth of the forest around the house could be described as irreversible. It is too late for the house owner to do anything to stop the trees growing.

Although if he cut down all the trees then maybe he could reverse it, but that would be harmful to the environment and against the law, so really there's no reversing it!