With the recent release of Fedora 23, Fedora 21 will officially enter End Of Life (EOL) status on December 1st, 2015. After December 1st, all packages in the Fedora 21 repositories will no longer receive security, bugfix or enhancement updates, and no new packages will be added to the Fedora 21 collection.
Looking back at Fedora 21
Fedora 21 was the first release to ship the Workstation, Server and Cloud editions when it was first released in December 2014. Fedora 21 Workstation was when users could first test GNOME Wayland, which is slated to be the default display server come Fedora 24. On the Server, Cockpit and Rolekit both made their debut in Fedora 21, and Fedora Cloud introduced the Fedora Atomic Host for the first time in Fedora 21.
About the Fedora Release Cycle
The Fedora Project provides updates for a particular release up until a month after the second subsequent version of Fedora is released. For example, updates for Fedora 22 will continue until one month after the release of Fedora 24, and Fedora 23 will continue to be supported up until one month after the release of Fedora 25.
The Fedora Project Wiki contains more detailed information about the entire Fedora Release Life Cycle, from development to release, and the post-release support period.