Thermodynamics process and cycle

Process 

Change of state is known as process.

Processes are classified into two types 

1. Reversible process: A process when reversed in direction follows the same path that of the forward path without leaving any effect on the system and surroundings.
   
2. Irreversible process: A process when reversed in direction doesn't follow the same path that of forward path by leaving traces of its effect on the system and surroundings. A process which is not reversible is known as irreversible process.
   

(imagine and feel while reading so that you can understand the concept)

Cycle

A system is said to have undergone a cycle when the initial and final points are same. For a cycle change in property is zero. A cycle is classified into reversible and irreversible cycle.

1. Reversible cycle: A cycle is said to be reversible if each and every process of the cycle is reversible. Reversible cycle is possible only in case of friction less quasi static process.i.e., a slow steady friction less process. There are no losses in a reversible cycle. Imagine a reversible adiabatic system where consider a insulated(no heat transfer takes place between cylinder and surroundings and is a slow friction less process ) cylinder with piston when compressed air inside the cylinder gets heated and when expanded the temperature decreases steadily and reaches to the original point. Here in this cycle initial and final points are same without effecting the surroundings.
2. Irreversible cycle: Even if single process is irreversible then it is said to be irreversible cycle. There are losses due to  friction, heat transfer. For example internal combustion engine where heat transfer takes place between cylinder and surroundings continuously.