Code releases are broken down into Releases, Versions, and Modifications. Releases are major changes in the way the system works. Expect major surprises when R changes. Versions may add features, fix bugs, and so on. Expect mild surprises in V changes. Modifications are generally bugfixes or very minor new features. No surprises should be expected when M changes, if there even is an M release. For any given Release, the Version should also be specified. The use of a Mod specifier is needed only when a mod is released.
It's also important to distinguish between Release and release. A Release is obviously when a big change happens that bumps the R number. A release is any tarball of the source code given out to the general public, however this usage should be avoided. Rather, speak in terms of Releases, Versions, or Mods.