Definitions and concepts in the field of hearing impairment. Hearing impairment: less than normal hearing resulting from auditory disorders: term preferred by federal government. Hearing sensitivity loss: poorer than normal auditory sensitivity for sounds; usually measured in db (decibels) using pure tones. Deaf: limited or absent hearing for ordinary purposes of daily living. Inappropriate to use in reference to mild or moderate hearing loss. Hard of hearing: person who has hearing loss but uses auditory channel as primary avenue for oral communication. The anatomy of the auditory system: ear is divided into four sections. Outer ear: most visible part of ear, useful in funneling sound to ear canal and in localizing source of sound. Middle ear: air-filled space behind eardrum that contains three tiny bones that carries sound to inner ear. Inner ear: snail-shaped part of ear (cochlea) containing organs of hearing and balance.