Push-to-talk operation

Push-to-talk operation (PTT): In telephone or two-way radio systems, that method of communication over a speech circuit in which the talker is required to keep a switch operated while talking.

Note: In two-way radio, push-to-talk operation must be used when the same frequency is employed by both transmitters. For use in noisy environments, or for privacy, some telephone handsets have push-to-talk switches that allow the speaker to be heard only when the switch is activated. Synonym press-to-talk operation.

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