Fuller's Earth describes types of clay that have absorbing and bleaching properties. The name comes from traditional textile workers cleaning or "fulling" wool with this clay. It consists mainly of the clay mineral called palygorskite (that's different both from kaolin or bentonite) or some type of bentonite (mainly calcium montmorillonite).
In cosmetic products, Fuller's Earth is used as an absorbent that can suck up excess oil from the skin. It's excellent absorbent properties also mean that too much of it can dry out the skin, so just like with bentonite, use it for good measure and moisturize after it.