1 Answers
Debian releases do not follow a fixed schedule. Recent releases have been made roughly biennially by the Debian Project.
Debian always has at least three release branches active at any time: "stable", "testing" and "unstable". The stable release is the most recent and up-to-date version of Debian. The testing release contains packages that have been tested from unstable. Testing has significantly more up-to-date packages than stable and is a close version of the future release candidate for stable. The unstable release is the release where active development takes place. It is the most volatile version of Debian.
When the Debian stable branch is replaced with a newer release, the current stable becomes an "oldstable" release. When the Debian stable branch is replaced again, the oldstable release becomes the "oldoldstable" release. Oldoldstable is eventually moved to the archived releases repository.
The most recent version of Debian is Debian version 11, codename "Bullseye". The next up and coming release of Debian is Debian 12 codename "Bookworm".