Severity of Defect

Severity:

          Severity means how much severe is the particular defect in the application (i.e.) how it affects the functionality of the application
Def:  The degree of impact that a defect has on the development or operation of a component or system.

Levels of Severity:

• Feature
• Trivial
• Text
• Tweak
• Minor
• Major
• Block
• Crash

Feature/Enhancement: 
            A feature request. request for a new feature or change in functionality for an existing feature

Trivial:
           This is a bug, but it doesn't really cause problems. cosmetic problem like misspelled words or misaligned text

Text: consistency of font

Tweak: Bug affects everyone.

Minor:
           Bug that bothers a few people. minor loss of function, or other problem where an easy workaround is present

Major:
            Bug affects an area of MediaWiki that is important on WMF sites. major loss of function

Block: 
          Other bugs can't be fixed until this one is. blocks further development and/or testing work. Unlikely unless testing directly from SVN

Crash/Critical: crashes, loss of data (internally, not your edit preview!)