The "trunk" series represents the primary line of development rather than a stable release branch. This is sometimes also called MAIN or HEAD.
Trusty Tahr, 14.04 LTS branch
Stable progress for Ubuntu 12.10, Quantal Quetzal.
Stable branch for Ubuntu 12.04, Precise Pangolin.
Stable branch for Ubuntu 11.04, Natty Narwhal.
Stable branch for Ubuntu 10.10, Maverick Meerkat.
Stable branch for Lucid Lynx. Updates to translations may be placed here, if necessary; they could be released for one of Lucid's four point releases.