If the effects produced by a process on the system as well as on the surrounding can be completely restored to their initial states and no changes are left in any of the system taking part in the process or in the surroundings then the process is said to be a reversible process. 

The process taking place slowly in controlled manner, all the mechanical process taking place under the action of conservative force are reversible. In reversible process, a system can retrace in the opposite direction so that it passes through exactly the same states in all respect as in the direct process.