Hifi and Hi-fi

Hi-fi and hifi are semantically related in stereo system topic. In some cases you can use "Hi-fi" instead a noun "Hifi", when it comes to topics like turntable, machine for playing record albums, sound equipment.

Hi-fi noun - The reproduction of sound with little or no distortion.

Hifi and hi-fi are semantically related in sound equipment topic. You can use "Hifi" instead a noun phrase "Hi-fi".