Sound Levels -- Meausred in decibels, sound levels refer to an acoustic wave's  effect on air molecules. Sound must be transmitted by molecules, but not necessarily air. In musical instruments, for example, it can be transmitted by the wood or brass. Sonar transmits sound through water.

Specific Language Impairment (SLI) - difficulty with language or the organized-symbol system used for communication in the absence of problems such as mental retardation, hearing loss, or emotional disorders.

Speech - spoken communication.

Speech Disorder - any defect or abnormality that prevents an individual from communicating by means of spoken words. Speech disorders may develop from nerve injury to the brain, muscular paralysis, structural defects, hysteria, or mental retardation.

Speech Processor - part of a cochlear implant that converts speech sounds into electrical impulses to stimulate the auditory nerve, allowing an individual to understand sound and speech.

Speech-Language Pathologist - health professional trained to evaluate and treat people who have voice, speech, language, or swallowing disorders (including hearing impairment) that affect their ability to communicate.

Sudden Deafness - loss of hearing that occurs quickly due to such causes as explosion, a viral infection, or the use of some drugs.
Tinnitus - sensation of a ringing, roaring, or buzzing sound in the ears or head. It is often associated with many forms of hearing impairment and noise exposure.

Receiver - the part of the hearing aid that sends the amplified sound into the ear.

Vent - a hole or holes in a hearing aid that allow air and some sound to pass through. This can be to reduce the Occlusion effet, to allow some sounds to pass through for people who do not need amplification at all frequencies, to prevent moisture build up, and to allow people to hear their own voice without an echoing effect.

Vestibular Neuronitis - infection at the vestibular nerve.

Vestibular System - system in the body that is responsible for maintaining balance, posture, and the body's orientation in space. This system also regulates locomotion and other movements and keeps objects in visual focus as the body moves.

Vestibule - bony cavity of the inner ear.

Vibrotactile Aids - mechanical instruments that help individuals who are deaf to detect and interpret sound through the sense of touch.

Waardenburg Syndrome - hereditary disorder that is characterized by hearing impairment, a white shock of hair and/or distinctive blue color to one or both eyes, and wide-set inner corners of the eyes. Balance problems are also associated with some types of Waardenburg syndrome.