Flutter is Google's open-source UI toolkit for building natively-compiled applications for mobile, web, and desktop from a single codebase, using the Dart language. Its distinctive approach is rendering its own UI (not using native components), giving consistent, customizable, high-performance interfaces.
What Flutter is
Flutter = a cross-platform UI framework (by Google):
→ ONE codebase → iOS, Android, web, desktop (Windows/macOS/Linux)
→ uses the DART language
→ builds NATIVELY-COMPILED apps (compiles to native ARM code for mobile)
→ everything is a WIDGET (composable UI building blocks)
