It's not often we see Apple release iOS software updates in the early hours of a Saturday morning, but that's what has happened with iOS 11.2.
Apple released iOS 11.2 shortly after 12:00 PST this morning. The update is available to the iPhone 5s and later, iPad Air and later, and the iPod touch 6th generation.
To download iOS 11.2, go to Settings > General > Software Update on your iOS device.
As for why this update was pushed out early Saturday morning, it appears that one of the bugs squashed in this update is one that would cause iOS to repeatedly crash on December 2, 2017. The bug was related to local notifications, which Apple says you should completely disable to avoid the bug if you're on an iOS version earlier than iOS 11.2.
There are several other new features included with the update to iOS 11.2. Apple Pay Cash support is included, but it's said that the feature won't actually go live until early next week, likely when iOS 11.2 was originally slated to be released. The update to iOS 11.2 also adds faster 7.5W wireless charging for the iPhone 8, iPhone 8 Plus, and iPhone X.
Some of the other notable changes in iOS 11.2 include three new live wallpapers for iPhone X, improved video camera stabilization, support for downhill snow sports in HealthKit, improved VoiceOver stability, and a fix for Calculator app bug where typing numbers rapidly could lead to incorrect results.