"Bootstrap" in web development refers to a free and open-source front-end framework designed to simplify and accelerate the process of developing responsive websites and applications. It provides a collection of CSS and JavaScript components, such as navigation bars, modals, and grid systems that help developers create visually appealing and functional designs without building from scratch. By facilitating consistent styling and cross-browser compatibility, Bootstrap significantly reduces development time while enabling the creation of mobile-friendly interfaces easily adaptable to various screen sizes.