DTMF

allocation of a unique tone to each button on an appliance (made up of two frequencies - high and low) that allows a computer to recognize the tone

Dual-tone multi-frequency (DTMF) signaling is used for telephone signaling over the line in the voice-frequency band to the call switching center. The version of DTMF used for telephone tone dialing is known by the trademarked term Touch-Tone, and is standardised by ITU-T Recommendation Q.23. Other multi-frequency systems are used for signaling internal to the telephone network.
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Abbreviation for dual-tone multifrequency (signaling) .

Dual Tone Multi Frequency

DATA TONE MULTIPLE FREQUENCY. DUAL TONE MULTIFREQUENCY. DTMF