(That was taken directly from the site I go to)
The youma are monsters that are capable of shape shifting that live by feeding off human organs. The Claymore are capable of seeing through their disguises and are able to kill them. The Claymore are given their name by the people because of the giant claymores they use.
There is a lot of blood and violence in this show. Heck, if I remember correctly there isn't a single episode that doesn't have blood and violence somewhere in it.

I highly recommend this show to anyone who can handle blood in anime.
(Posted specifically for Typheus
