Bootstrap is a free and open-source CSS framework that is directed at responsive, mobile-first front-end web development). It contains HTML, CSS, and JavaScript-based design templates for typography, forms, buttons, navigation, and other interface components. Bootstrap is designed to simplify the development of informative web pages, as opposed to web applications). The primary purpose of adding Bootstrap to a web project is to apply its choices of color, size, font, and layout to that project. Once added to a project, Bootstrap provides basic style definitions for all HTML elements).

Bootstrap was developed by Mark Otto and Jacob Thornton at Twitter as a framework to encourage consistency across internal tools). Before Bootstrap, various libraries were used for interface development, which led to inconsistencies and a high maintenance burden. Bootstrap was created to solve these problems and provide a consistent and easy-to-use framework for web development.

Some key features of Bootstrap include:

• Responsive design: Bootstrap is designed to be responsive, meaning that it can adapt to different screen sizes and devices.
• Grid system: Bootstrap includes a powerful grid system that allows developers to easily create complex layouts.
• Pre-built components: Bootstrap includes a wide range of pre-built components, such as buttons, forms, and navigation menus, that can be easily customized and used in web projects).
• JavaScript plugins: Bootstrap includes a number of JavaScript plugins that can be used to add interactivity and functionality to web pages).

Bootstrap is widely used by web developers and designers, and is the most popular CSS framework for developing responsive and mobile-first websites. It is also highly customizable, with many options for changing the default styles and behavior of its components).