What does "hardy" mean in /etc/apt/sources.list?
Hardy is the name of the 8.04 Release, "Hardy Heron".
Each Ubuntu Release follows the same pattern, year.month numbers for versioning, e.g 8.04 8.10, 10.04 (usually 2 releases every year) and a code name.
Ubuntu Releases are:
- 4.10 - Warty Warthog
- 5.04 - Hoary Hedgehog
- 5.10 - Breezy Badger
- 6.06 - Dapper Drake
- 6.10 - Edgy Eft
- 7.04 - Feisty Fawn
- 7.10 - Gutsy Gibbon
- 8.04 - Hardy Heron
- 8.10 - Intrepid Ibex
- 9.04 - Jaunty Jackalope
- 9.10 - Karmic Koala
- 10.04 - Lucid Lynx
They appear on your sources list to indicate which release(version) of the repository you are using.
PS: You must have also realized by now, that Ubuntu releases follow an alphabetical naming order, always using an adjective and an animal name. The next Ubuntu release (10.10) will be named Maverick Meerkat.
PS2: The oficial Ubuntu page with all codenames, plus some discarded alternatives names can be found here, if you are curious about it.