Real Dictionary

audio
Audio equipment is used for recording and reproducing sound.

audio in American English
of frequencies corresponding to sound waves that can normally be heard by the human ear
adjective: designating an electronic apparatus using audio frequencies
noun: the audio elements of television (distinguished from video)

audio in British English
adjective: of or relating to sound or hearing
noun: the element of sound in a broadcast or recording

audio- in American English
hearing or sound
combining form: a combining form used in the formation of compound words, with the meanings: “sound within the range of human hearing” (audiometer); “hearing” (audiology); “sound reproduction” (audiophile)

audio- in British English
combining form: indicating hearing or sound