What term describes the use of a sub-audible tone transmitted along with normal voice audio to open the squelch of a receiver?

CTCSS stands for Continuous Tone-Coded Squelch System. It is a system that superimposes a continuous, low-frequency (sub-audible) tone on your transmitted voice audio. Repeaters often use CTCSS to keep their receivers muted until they hear a signal with the correct matching tone, preventing random noise or distant stations from accidentally triggering the repeater. While CTCSS uses sub-audible tones, DTMF (Dual-Tone Multi-Frequency) refers to the audible keypad tones, similar to a traditional telephone, used for sending commands. 'Carrier squelch' simply opens the receiver's audio based on the raw strength of the incoming radio frequency signal, without requiring any special tone at all.