An activity in Android is an application component that provides a screen with which users can interact to perform a specific action, such as dialing a phone number or viewing a map. It represents a single screen with a user interface, similar to a window or frame in other programming languages. The Activity class is a crucial component of an Android app, and the way activities are launched and put together is a fundamental part of the platform's application model. An app can have several activities, and the user can switch between them during the runtime of the application. Activities have a lifecycle with various callback methods that allow the app to manage its state and behavior, such as onCreate(), onStart(), onResume(), onPause(), onStop(), and onDestroy