What do you mean severity and priority of bugs in software testing?

Bugs severity means the degree of error impact on operations. There are four category of severity:

1. Critical: It causes failure of software system, subsystem or any program of the software. It causes loss of critical data.
2. High: It does not cause failure but causes system to produce incorrect, incomplete, inconsistent results and impairs usability.
3. Medium: It does not cause failure, it does not impair usability and does not influence in the fluent work of the system.
4. Low: It is an aesthetic bug, or is a result of non-conformance to standard.

Bugs priority deals with the urgency of resolving. These are also of four kinds:

1. Immediate: It should be resolved immediately.
2. High: These are resolved before the release of software and are solved as soon as possible.
3. Medium: These are repaired after some serious bugs are resolved.
4. Low: It can be resolved in major software revision or may not be resolved at all.