As far as I know (or can remember it being explained to me) is that Endometriosis is the condition/illness where the endometrium that lines the uterus sheds not only inside the uterus but also outside of the uterus. Since the blood has no where to go, it causes the lesions and scar tissue that in turn causes the pain.

Never heard the term metioses, but that doesn't mean it can't happen!