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?

It holds the highest utility and efficiency while the processes are scheduled and each part is systematically saved when an interrupt happens.