Flutter is an open-source mobile application development framework created by Google. It is used to develop applications for Android, iOS, Windows, Mac, Linux, Google Fuchsia, and the web from a single codebase. Flutter apps are written in the Dart programming language and make use of many of the same APIs as Android and iOS.
For example, a Flutter app might use Material Design for Android and Cupertino widgets for iOS to give the app a native look and feel on each platform. Additionally, Flutter apps can make use of platform-specific APIs such as the camera or Bluetooth.