Hearing or sound.
[Latin audire, to hear.]
Audiometry is measurement of the range and sensitivity of a person's sense of hearing; audiology is the branch of science and medicine concerned with the hearing; the adjective is auditory. As a free-standing word, audio refers to sound, especially sound that has been recorded, transmitted, or reproduced. Several related compounds exist, such as audio-visual (often now without the hyphen), using both sight and sound, as in a slide-tape or video presentation; audiobook, a recording of the reading of a book; and audiophile, a hi-fi enthusiast.