Flutter is an open-source UI framework developed by Google that allows developers to create high-performance, cross-platform mobile applications with a single codebase.

A UI kit provides developers with a set of reusable components that can be easily integrated into a website or application. These components are pre-designed with consistent styling and functionality, allowing developers to save time and effort in the design and development process. UI kits can be either custom-built or third-party, and often include components for buttons, forms, typography, icons, and more.