Official Description: Android Lifecycle-Common

CommonsWare’s Notes

This artifact contains some of the base classes that implement the Jetpack lifecycle framework, including Lifecycle and LifecycleOwner. Frequently, you will not depend on this artifact directly, but instead get it through transitive dependencies on higher-level constructs, such as the LiveData artifacts.

As with many pieces of the Jetpack, Lifecycle and related classes debuted with the Architecture Components. If you see blog posts and other materials referring to classes in the android.arch package, that is the Architecture Components. The concepts from the Architecture Components implementation are likely to remain the same in the newer Jetpack classes, but the APIs are likely to be different.