Frequency divider

how

normally a technical device to simply cut down the input frequency to half of the input frequency

use

used on full polyphonic synthesizers and organs to get full polyphonic by using just one main oscillator or one per octave and get the other notes / frequencies by dividing them from the main oscillator. so on most early full polyphonic synths / organs 12 oscillators were needed to get a chromatic scale generated over the keyboard.