The rear portion of a guitar body. On a solidbody electric guitar, the back will be a thick slab of solid wood, often mahogany, ash, or alder. It is a major contributor to the tone, resonance, and sustain of the guitar.
On an acoustic guitar, the back will be a thin sheet of solid or laminated wood, often rosewood or mahogany. The back forms the rear surface of the guitar’s acoustic chamber and supports the resonance of the guitar, working in concert with the guitar’s top.