Official Description: The Support Library is a static library that you can add to your Android application in order to use APIs that are either not available for older platform versions or utility APIs that aren't a part of the framework APIs. Compatible on devices running API 14 or later.

CommonsWare’s Notes

AppCompat is a way to get a consistent Material Design look across Android OS versions, particularly to versions older than Android 5.0.

While there are dozens of classes in this artifact, the only one that you will work with directly (usually) is AppCompatActivity. If you have your activity inherit from AppCompatActivity, you are requesting to use AppCompat and to adopt the Material Design look.

If you inherit from AppCompatActivity, you also need to: