Definition and background:
The resonator of a stringed instrument or some percussion instruments. The term also applies to the electronic versions of stringed instruments that are solid to avoid the unwanted sound from the resonator. That part of a wind instrument that remains after the removal of the mouth piece, crooks, and bell. The tube of an organ -pipe above its mouth.
For more information on the music term "Body" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary