Heterodyne

1. To generate new frequencies by mixing two or more signals in a nonlinear device such as a vacuum tube, transistor, or diode mixer.

Note: A superheterodyne receiver converts any selected incoming frequency by heterodyne action to a common intermediate frequency where amplification and selectivity (filtering) are provided.

2. A frequency produced by mixing two or more signals in a nonlinear device.

Source: from Federal Standard 1037C and from MIL-STD-188