Ubuntu is one of the most popular linux distro. Ubuntu releases every six months. Year and month of its release into the name of Ubuntu’s own example 9:10 means Ubuntu release month to 10 months of the year 2009.
Here is Ubuntu that has been released:

Ubuntu 6.06 Dapper Drake (Desktop and Server)
Ubuntu 6.10 Edgy Eft
Ubuntu 7.04 Feisty Fawn
Ubuntu 7.10 Gutsy Gibbon
Ubuntu 8.04 Hardy Heron
Ubuntu 8.10 Intrepid
Ubuntu 9.04 Jaunty Jackalope
Ubuntu 9:10 Karmic Koala (Desktop and Server)
Ubuntu 10:04 Lucid Lynx
Ubuntu 10.10 Maverick Meerkat (Desktop and Server)

http://www.ubuntu.org