Posted by colby
Debian GNU/Linux (Website) has a versioning scheme different from most other distributions. Rather than releasing one official version frequently (every few months) and a beta prior to that sometimes, debian releases one tried and true version fairly infrequently and operates a few other "repositories".
At any time, there is a stable version. This version has undergone hardcore testing. Any new package updates also undergo testing and new versions are rolled in only if they are bugfixes. Security updates are only maintained for this version. This is the version generally used for servers.
At the same time, there is an "unstable" version. This version always has the latest packages from the maintainers. These packages are tested but not heavily (they compiile, run, but are not necessarily robustly tested) -- properly packaged, but not guaranteed to provide stability. This version is not generally used except if you might need a "bleeding edge" version of a package.
The third semi-constantly maintained version is the "testing" version. This version has fairly recent stuff, decently tested. There are no security updates released for this version either. This is the "stable" version of tomorrow, after it passes through a "frozen" state (see below). This is what most people use for workstation-class machines.
The only occasional version is "frozen". This is the version that happens inbetween "testing" and "stable". When the project determines a release should be frozen, no new packages are accepted, bugs are fixed, and then the set of packages in testing get rolled into "frozen". Frozen gets the crap tested out of it, and then it becomes "stable".
So, if you want to run a server, try stable. If you want a workstation, try testing. If you want to be on the edge, run a mix of testing/unstable.