Flutter is not a programming language. It's a software development kit (SDK) with prewritten code, consisting of ready-to-use and customizable widgets, as well as libraries, tools, and documentation that together serve to build cross-platform apps.
Flutter is one of the best solutions to develop apps for Android and iOS, without having to write in a different codebase for each platform. Using the same codebase, it is also possible to create web apps for browsers as well as native programs for Windows, Linux, and macOS.
Flutter forms the UI component of Google's upcoming operating system, called Fuchsia.
Flutter SDK, setting up Android Studio to develop Flutter-based applications, the architecture of Flutter framework and developing all types of mobile applications using Flutter framework.