A jointed thing has joints — the little places where two parts meet — and it can bend or move there on purpose. A jointed doll can sit and wave because the arms and legs are made to fold at the shoulder, elbow, hip, and knee, the way a body does. Insects have jointed legs. Some pipes, folding rulers, and robot arms are jointed too. We use the word about bodies, toys, tools, and machines when that bending is built in, not when something has merely been stuck together. Though actually, jointed is easy to mix with joined. Joined only means “put together.” Two tables pushed into one are joined; they are not jointed unless they fold at a hinge. The same spelling is also the -ed form of the verb joint, a kitchen or workshop word: you can joint a chicken (cut it at the joints) or joint two pieces of wood (fit them at a joint). That is a different job. The picture learners need first is the adjective: made with joints, so it can bend.