Is there any difference between Bug and Defect ?

Question

how do we give the severity and priority to the bugs?

Answer 1

Bug: Deviation in software implementation.
Defect: Deviation in functionality.
A bug may leads to a Defect.

Answer 2

Its a philosophical question anyway a bug is the result of a coding/manufacturing/documentation error while a defect is a deviation from the requirements.

A defect does not indicate that its a bug as it may not have been implemented.