I was just reading a blog that concerned the origin of the name Darth, and I was shocked at how when someone said "Dark Jedi" it ment that they were a Sith. I always thought that the Sith were a species of their own, and a Force-Sensitive species at that, liek the Miraluka. Can someone clarify this for me?

And also, how weird is it that the Miraluka and the Sith, thw two Force-Sensitive species are both wiped out.