MUI, formerly known as Material-UI, is an extensive library of React components implementing Google's Material Design. It offers a variety of pre-designed components ranging from buttons to grids, enhancing development speed and efficiency. The framework supports theming and customization, allowing developers to adhere to their unique design specifications while ensuring a consistent look and feel across applications. Ideal for web and mobile applications, MUI emphasizes accessibility and responsiveness, making it an excellent choice for a diverse range of use cases including enterprise applications, dashboards, and personal projects.