What is a framework?

I think the basic difference between library and framework is that if you use framework it's responsible for bootstrap of your application, and library does not.

But also framework drives structure of result codebase - filenames convention, directory structure, maybe way you implement your features.

To me framework is a set of libraries, glued together with some infrastructure code. Framework provides some conventions that speed up most common tasks.

It may be possible to use framework as a library, though there is no or small benefit.