2.48a vs 2.48b vs 2.48.2 vs... somebody please clarify

Lately I’ve been seeing a lot of references to ‘b’ and ‘.2’ versions. I can’t even get a search hit on this forum for 2.48.2 Where is are these denominations coming from?
2.48a I understand, because it’s the current official release from Blender.org. (frozen from further development)

Are ‘b’ and ‘.2’ versions just homemade shorthand for the ongoing SVN available on graphicall? :eek:

Blender has a subversion number that appears in the header, but this does not relate to releases (not to be confused with SVN revision number).
This is important so blenders file reading code knows exactly what data should be converted and what has already been updated, checked- like particles, changes in the game engine, new armatures, new options that need to be enabled by default to keep old behavior etc.

its just blenders internal version tracking so blend files can be used by people who update blender frequently (every day or week).