As someone else pointed out, see:
http://www.debian.org/releases/
I have heard someone say a good naming system would be:
"stable" = "server" (well tested, very stable, but old versions of everything)
"testing" = "workstation" (newer programs, a few bugs but pretty stable)
"unstable" = "geek" (the latest available stuff, but can have major problems crop up that is difficult for a new user to fix)