A UI framework is a collection of pre-written code and tools that help developers create user interfaces for applications more efficiently. These frameworks provide a structured way to design and build the visual elements of software, such as buttons, menus, and forms, ensuring consistency and usability across different platforms. Popular UI frameworks include React, Angular, and Vue.js. They offer features like reusable components, responsive design, and built-in styling options, allowing developers to focus on functionality rather than starting from scratch. By using a UI framework, developers can save time and improve the overall user experience of their applications.