Setting aside the nearly religious preferences I know exist; what is the practical difference between #GNU #Linux and #Unix #BSD?

I started with Mandrake in 2001 and lost count of which and how many systems distros I’ve used since then. But the stand outs for me have been #Mandrake, #Fedora, #Suse, #OpenDarwin, and #GNUStep. While there were differences between the systems in terms of hardware and software support I have never grokked what differentiates BSD and GNU.