DTMF (Dual-tone multi-frequency) tones are the sounds generated by touch tone phones. When a key on a phone keypad is pushed not one but two different frequencies are generated, hence the name dual tone multi frequency. DTMF is also known as tone dialing as opposed to the older pulse dialing.
Each of the 12 keys on a touchtone phone generates a different DTMF. String together the various DTMF tones and you can dial a number. There may be occassions when you need a dial tone. (hint, hint)
click to hear each DTMF tone
Each DTMF tone is 1 second long. To simulate dialing a number on a phone keypad, play the individual DTMF tones in the correct sequence. Or right-click each button and download the tone.
If you're interested in DTMF tones you probably want to read about blue boxes and silver boxes too.