Debian has basically 3 current branches

Stable == (Currently called Woody)Stable package list and versions. Sometimes people say Stable == Old. Really it means that Stable means just that Few changes barring Security or Major Data Loss bugs. Basically in Maintenance mode.

Testing == Next version of Stable (currently called Sarge), Supposed to always be in an installable state (not always the case) Package list can be very volatile. But can become very stable at other times. Currently this testing is is shooting for a frozen Around Middle of April. Also, testing has versions of the software some would condsider very good and recent.

Unstable == Unstable. Unstable as the packages are in a constant state of flux. On a a long 4 day weekend, Monday can have as many as as many as 500 packages updated. But, when you understand that something like Postgres in Debian is split into something like 11 packages, versus typically 2 for RedHat or SuSE or Mandrake. Unstable is where there is the latest and greatest software typically. I would also call this the branch for those who understand the Debian dpkg/dselect/apt systems.

Okay, so I lied, there is actually 4 branches.

Experimental == Major packaging changes, experimental versions of the package versions of things that would not build properly automatically, etc... basically pre-bleeding edge. This is not an "instabllable" branch. You have to include it along with piece from Sid or Sarge.

and On the Naming etc...

Potato == Debian version 2.2 No longer being Maintained Former Stable. DO NOT USE THIS ONE.

Woody == Debian version 3.0 Being Maintained as Stable

Sarge == Debian v3.1(or 4.0) or the Next Version of Stable still in a State of Flux

Sid == Debian Unstable (will always be too), unstable terms packages are unstable, rapid versioning not unstable as in crashing... alothough this is bound to happen with rapid versioning.

(____) == Experimental doesn;t have a named version.