Material Components for the Web (MDC Web) is a modular and customizable UI library for building modern web applications. It implements Google's Material Design, providing components like buttons, cards, dialogs, and menus. MDC Web emphasizes accessibility, performance, and cross-browser compatibility. The library aims to offer a cohesive and visually appealing user experience, allowing developers to easily integrate Material Design principles into their projects with a focus on customizability and theming.