The term 'Sound Mixer's Control' refers to a device known as a fader, which is a five-letter word. A fader is a type of control used in audio mixing, which allows the user to adjust the volume of a particular sound source. It is typically used to adjust the balance between multiple sound sources, allowing the user to create a desired mix. Faders are also used to adjust the overall volume of a mix, allowing the user to make subtle adjustments to the overall sound.