I would say: - a framework provides a structure you fit your stuff into or build off of - a library provides functionality you can fit into the structu

I would say: - a framework provides a structure you fit your stuff into or build off of - a library provides functionality you can fit into the structure of your code however you see fit In the case of bootstrap, I think they use the term framework because it supplies layout and styling patterns you fit your page/app into. E.g., the grid, containers, forms with form-groups, the predefined "primary", "secondary", ..., styles, etc.