Flutter is an open-source mobile application development framework that was created by Google. It allows developers to build high-quality, cross-platform mobile applications for both Android and iOS using a single codebase. The framework utilizes the Dart programming language, which was also created by Google, and provides a robust set of widgets and tools to simplify the development process.

One of the main advantages of Flutter is its ability to provide a native-like experience on both Android and iOS platforms. This is achieved through the use of its own rendering engine and widgets, which allows for consistent performance and a unified user experience across devices. Additionally, Flutter's "hot reload" feature makes it easy to iterate on app designs and fix bugs quickly, reducing development time and improving overall efficiency. With its ease of use, flexibility, and growing community, Flutter has become a popular choice for building mobile applications of all types and sizes.