Difference b/w Service Request & Incident?

Hi Experts,

Would you please explain me what is the difference between Service Request(SRVR) and Incident(ITIN)?

In which situation, these two documents are used? 

I am confused as both these transaction types have the same leading transaction categories and business transaction categories.

Please clarify my confusion with your inputs with a good example.

Awaiting for your response.

Regards

Maddy