A cochlear implant is a small, complex electronic device that can provide a sense of sound to a person who is profoundly deaf or has severe hearing loss. The implant transmitter is placed behind the ear, and the receiver is surgically placed under the skin.
Cochlear implants are different from hearing aids. Hearing aids amplify sounds, while cochlear implants bypass damaged portions of the ear and directly stimulate the auditory nerve. [From nidcd.nih.gov]