Linux isn’t an OS. It’s just a kernel, which doesn’t do much like it self. GNU is an OS and Linux is one of its kernels.
Yeah thanks sherlock… But it’s quite a common simplification and understood by almost anyone.
Edit: I’m sorry – after reading my comment again– that came across quite a bit harsher than it was meant.
Considering that Hurd is still not finished what other kernel does GNU use other than Linux?
HURD is the default GNU kernel. From what I here there are also GNU systems running on BSD’d stuff, and I suspect they’re are many GNU systems running with Kernels users have created themes, whether for very specific use cases or just for fun. I recall following someone’s blog an Diaspora* about the latter a year ago until she got bored with it.