Call duration is the length of time that the phone rings before it is picked up. The longer the call duration, the more likely you are to get through.
When you make a call on the phone, you can actually hear the connection being made. If you have the right equipment, you can even see the caller ID on your phone. This is how you know whether or not someone has called you back. It is called “call duration” because it takes some time for the call to be connected and to get to the person you are calling.