Debian's 'production' release.
Currently 'Woody' (3.0r1) as of 11/8/2003.
Debian testing every so often goes through a feature freeze, has all the bugs worked out of it, and then is released as stable. After that, only security updates (backported to the versions of software IN stable) are released.
Stable is as stable suggests. You'd have to try hard to break it.
To get new software on Stable, see BackPorts.
4 pages link to Stable:
