Apple is releasing minor OS updates to its installed base today, starting with a bug-fix focused watchOS 2.2.2 update for the Apple Watch and continuing with iOS 9.3.3, which appears to include a bunch of bug fixes and unspecified performance improvements. The update can be applied on your device over-the-air in Settings → General → Software Update or downloaded through desktop iTunes.
The update is available for the iPhone 4s and later, the fifth-generation iPod touch and later and iPad 2 and later. The update includes bug fixes for Calendar, FaceTime, Safari, Siri Contacts, Web Media, WebKit, the iOS kernel and other parts of the system.
For more detailed information about these fixes, see Apple’s support document.