Refers to sound in a technical or media context, often as opposed to video. Used in compounds like オーディオ機器 (audio equipment).
This TV has an audio output terminal.
audio equipment; stereo system
Often implies high-quality or enthusiast-grade sound systems. Can refer to the whole setup or individual components.
He has a collection of high-end audio equipment.
I like listening to audio in a quiet room.
He's very particular about his audio equipment and spent hundreds of thousands of yen on speakers alone.
My hobby is putting together my own audio system.
audio enthusiast; audiophile