Five state of process

New. The process is being created.
Running. Instructions are being executed.
Waiting. The process is waiting for some event to occur (such as an I/O completion or reception of a signal).
Ready. The process is waiting to be assigned to a processor.
Terminated. The process has finished execution.

Why the states are divided into 5, not 4, or 7? 

These names arbitrary,and they vary across operating system.The states that they represent are found on all systems,however.Certain operating systems also more finely delineate process states.