What are different severity ratings in a project?

There can be 4 types of severity ratings in a table:

i.) Severity 1 - Showstoppers - Don't allow application to move at all.

ii.) Severity 2 - Application continues with severe defects - Application works with these defects that might have severe implications.

iii.) Severity 3 - Application works with unexpected outputs

iv.) Severity 4 - Suggestions - These are improvements suggested in application. They don't affect performance of the application.