Bootstrap
In plain terms
A popular CSS/JS framework of prebuilt responsive components.
Going deeper
Bootstrap offers a grid system and ready-made components (buttons, modals, navbars) for quickly building responsive sites. It standardizes common UI patterns.
Under the hood
Its grid and components speed development but can make sites look generic; heavily class-based.
Examples
Admin dashboards, prototypes, responsive layouts, internal tools.
Think of it like...
Like a furniture catalog of matching, ready-to-assemble pieces for fast room setup.