Simplify the following text for a Grade 7 native English-speaking person.
Original: The portmanteau term `` Claymation '' is a registered trademark in the United States , registered by Will Vinton in 1978 to describe his clay-animated films .
Simplified: The word `` Claymation '' is a registered trademark in the United States . It was registered by Will Vinton in 1978 to describe his clay animation films .