Flutter is a mobile app SDK for building high-quality native apps on iOS and Android. Flutter is a Google product used by developers to create attractive and fast mobile apps. The main advantage of using Flutter is its cross-platform compatibility, which allows developers to create apps for both Android and iOS devices with the same code base. 

Flutter is based on the Dart programming language and uses the Skia graphics library. Flutter apps are built using the Dart programming language and the Flutter SDK. The Flutter SDK includes the Dart platform, the Flutter framework, and the Dart tools. 

Flutter apps are fast, responsive, and beautiful. They are also easy to develop and deploy. Flutter is an open-source project with a growing community of developers who are passionate about making mobile apps better.