For the More Curious: App Bar vs Action Bar vs Toolbar
You will often hear people refer to the app bar as the “toolbar” or the “action bar.” And the official Android documentation uses these terms interchangeably. But are the app bar, action bar, and toolbar really the same thing? In short, no. The terms are related, but they are not exactly equivalent.
The UI design element itself is called an app bar. Prior to Android 5.0 (Lollipop, API level 21), the app bar was implemented using the ActionBar class. The terms action bar and app bar came to be treated as one and the same. Starting with Android 5.0 (Lollipop, API level 21), the Toolbar class was introduced as the preferred method for implementing the app bar.
As of this writing, ...