it's a rough rule of thumb at best though – higher-order-functions or other things that take a callback blur the line a lot (IoC, what a sibling comment said). or say a library has an event-loop, or maybe does networking and you only provide some handlers – would that make it a framework?

i guess it's about frameworks being "the main thing happening". i.e. a framework controls the whole program's execution, occasionally yielding control to your code. which is a bit wordier to be sure :)