The difference between library and framework is quite subtle sometimes and in this case many use it interchangeably. You are correct though, jQuery themselves call it a library.

I don't agree to "does nothing to alter the language" though. It changes the way you manipulate DOM across your codebase. When one says 'library', I assume it's something you make calls to to achieve certain functionality. Like an image library or oauth library.

Also, that jquery is implemented in javascript is not relevant in my opinion. Rails is implemented in ruby. Does that make it not-a-framework?