What is the difference between Activity and AppCompatActivity?

AppCompatActivity is a subclass of Activity that provides compatibility with Material Design features and other modern capabilities on older versions of Android (below Android 5.0 Lollipop). AppCompatActivity includes built-in support for the action bar (Toolbar), themes, and styles of AppCompat.

AppCompatActivity offers:

• Toolbar support: Replaces the deprecated ActionBar, providing more flexibility and customization options.
• Theme compatibility: Applying the TextAppearance.AppCompat theme allows the use of Material Design fonts and colors on older devices.
• Fragment support: Ensures proper operation of fragments across different OS versions.

In simple terms, AppCompatActivity is an Activity with "backport" of modern features to ensure a consistent look and behavior of the app across all supported Android versions. In modern projects, it is almost always used.