Any change in the thermodynamic state of a system is called a thermodynamic process.
For example: In the above graph process 1-2 is a thermodynamic process.
Any series of thermodynamic state change in which the initial and final states of the system (thermodynamic system) are same is called a thermodynamic cycle.
For example: In the above graph series of thermodynamic state change 1-2-3-4-1 is called a cycle.
Quasi static process
An infinitely slow process which is a locus of equilibrium points is called a Quasi static process.
A Quasi static process is also known as reversible process.