About 30-40 years ago, our entertainment, was either watching TV or listening to CD music.
Music entertainment was provided in a "CD Component" or in a "Receiver" system.
A Mixer is a device in-between a "Player" on one side and an Amplifier on the other. The Mixer is built-in with 2 or 3 Mic inputs. The music played out from a Player and the Singer's vocal will go into this equipment, mix together and channel out to the Amplifier (Receiver)/Speakers.