Clay animation is one of many forms of stop motion animation. Each animate piece, either character or background, is "deformable"—made of a malleable substance, usually Plasticine clay. The portmanteau term "Claymation" is a registered trademark in the United States, registered by Will Vinton in 1978 to describe his clay animated films. While the word is not considered a genericized trademark, it has become a trademark which is often used generically in the US to refer to any animation using plasticene or similar substance.