What's the difference between crowns, full veneer crowns and jacket crowns?

All are crowns: A crown is a restoration that fully covers a tooth a full veneer is a crown whose outer surface is usually a porcelain material fused to an internal metal a jacket usually refers to a crown that is all porcelain.

Materials: A crown refers to a restoration that covers the exposed surfaces of the tooth that are visible to us. A full veneer crown typically has a metal understructure with porcelain covering it all around. A jacket crown is usually all porcelain. (the reference to these is mostly historic. The preparation for these is very aggressive. ).

Not much: Full jacket is just another name for a full coverage crown. Lots of names for one thing.