This is a process of connection between a computer and an ordinary phone. For example, one can call from Skype to a cell phone by dialing a specific number.
The function is available in some telephone networks and it allows
receiving the other call at the moment of the actual conversation by the method
of setting the active call in the waiting mode or cancellation. This will let
not to miss an important call and to agree upon time when it will be possible
to call back.