Division of guitars by material that are made
If we talk about the wood from which the body (corpus) of the instrument is made, we use the terms massive, semi-solid and plywood.
If we say that the guitar is a solid, it means that the whole body was made of one piece of wood.
At least some part of the body (front plate, back plate, ...) was made of one piece of wood.
Mostly several layers of wood (or laminate boards) are glued together.