Squelch

In telecommunication, a squelch is a circuit function that acts to suppress the audio output of a receiver.

Note: The squelch function is activated in the absence of a sufficiently strong desired input signal, in order to exclude undesired lower-power input signals that may be present at or near the frequency of the desired signal. Contrast with noise suppression[?].

Source: from Federal Standard 1037C and from the NTIA Manual of Regulations and Procedures for Federal Radio Frequency Management and from MIL-STD-188