Programmer - "Functional programming" has a clear meaning, but does "functional language"?

Programmer Question

I understand very clearly the difference between functional and imperative programming techniques. But there's a widespread tendency to talk of "functional languages", and this really confuses me.

Of course some languages like Haskell are more hospitable to functional programming than other languages like C. But even the former does I/O (it just keeps it in a ghetto). And you can write functional programs in C (it's just absurdly harder). So maybe it's just a matter of degree.

Still, even as a matter of degree, what does it mean when someone calls Scheme a "functional language"? Most Scheme code I see is imperative. Is it just that Scheme makes it easy to write in a functional style if you want to? So too do Lua and Python. Are they "functional languages" too?

I'm (really) not trying to be a language cop. If this is just a loose way of talking, that's fine. I'm just trying to figure out whether it does have some definite meaning (even if it's a matter-of-degree meaning) that I'm not seeing.