Debian

Debian is a Linux-based operating system.

Ubuntu is downstream.

Contents

Branches

The operating system is developed and maintained in branches:

Stable is the current release and receives periodic updates to software.
Oldstable is the previous release. It receives only security updates, and even then for just a year.
Testing is the next release. Kernels and software have been tested but not thoroughly, so both instability and frequent updates should be expected.
Unstable, codenamed Sid, is the active development branch. While it is expected to boot and run, code changes are checked in without testing.
Experimental is not even expected to boot and run.