Alongside OS X El Capitan 10.11.3, Apple has launched iOS 9.2.1 to all iPhone, iPad, and iPod touch users across the globe. The update is available via Settings > General > Software Update on your iOS device.
This update contains security updates and bug fixes, including a fix for an issue that could prevent the completion of app installation when using an MDM server.
According to the release notes, much like OS X 10.11.3, this update mainly contains bug fixes and security updates. The only notable update found in this release is a fix for a bug that could prevent app installation over an MDM server. You could also call this update iOS 9.2 v2, as this build most likely fixes bugs mainly found in iOS 9.2 which was released more than a month ago.