Bootstrap is a popular open-source front-end framework used for designing responsive and mobile-first websites. Developed by Mark Otto and Jacob Thornton at Twitter, the framework was initially released in 2011. Bootstrap provides a collection of HTML, CSS, and JavaScript components, such as navigation bars, modals, and carousels, that help accelerate web development. It is widely adopted for its ease of use, compatibility across various browsers, and a strong emphasis on responsive design. The framework also includes built-in support for flexible grid layouts, typography, and forms, making it a comprehensive toolkit for developers. You can learn more about Bootstrap and access its resources at [https://getbootstrap.com/](https://getbootstrap.com/).