A busy signal (or busy tone or engaged tone) in telephony is an audible or visual signal to the calling party that indicates failure to complete the requested connection of that particular telephone call.
There are several types of signals known as busy signals:
a reorder tone, (sometimes called a fast busy signal), indicates that no transmission path to the called number is available.
an otherwise unspecified busy signal indicates that the called number is occupied or otherwise unavailable
this tone sometimes occurs at the end of a call to indicate the other party has hung up. See disconnect supervision.
Many different countries have different signalling tones that act as "busy signals".
