Today Apple has released iOS 10.2.1, which comes about 42 days after iOS 10.2 was released. The description of the update simply says that it includes bug fixes and security improvements for the iPhone or iPad, so it's easy to tell that this is a minor update. The first iOS 10.2.1 beta was released on December 14th followed by a second beta on December 20th, a third beta on January 9th and a fourth beta on January 12th.
Most likely, this update fixes certain issues that were encountered following the release of iOS 10.2, which included new wallpapers for the iPhone 7 and 7 Plus, a new TV app, new Messages effects, new Camera settings, a new Videos app widget and 100 new emoji characters based on Unicode 9.0.
pple’s security page for iOS 10.2.1 says that the software update addresses under-the-hood kernel improvements and bugs that cause Auto Unlock to unlock when the Apple Watch is off the user’s wrist and issues with malicious contact cards that can crash the Contacts app. There is also a fix for an issue that causes an activation-locked device to be manipulated into briefly presenting the Home screen.
Source: forbes