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Audible ringing tone: In telephony, a signal, usually consisting of an audio tone interrupted at a slow repetition rate, provided to a caller to indicate that the called-party instrument is being sent a ringing signal.
Note: The audible ringing tone may be generated by the called-party servicing switch or by the calling-party servicing switch, but it is not generated by the called telephone instrument. It is generally started and stopped at the same rate as the ringing signal itself but perhaps out of phase.
Synonyms audible, ringback tone.
Source: from Federal Standard 1037C and from MIL-STD-188
