iOS 9.2.1 was just released today, and it's the first update to iOS 9.2. The last iPhone update was last month, which is how long iOS9.2.1 has been in the testing phase. There had been three beta versions of this update that were given to developers and beta testers.
You can download this update, like all other updates, over the air. It's just a minor update, mostly bug fixes.
According to the Apple Release, in addition to bug fixes, the update includes security improvements and a fix to an issue that affected some enterprise customers.
Here's the wording:
The next update will be more major, as it will be iOS 9.3. Developers have been given seeding versions of this for testing. The release of iOS 9.3 will be exciting because of a new Nigh Shift feature that will reduce the amount of blue light in low-light situations so that it affects your brainwaves less and allows for better sleep at night. There will also be new educational features, Quick Actions for 6S users, and more, in the 9.3 update.