Audio refers to sound. A conference is a meeting. Audioconferencing usually refers to meetings held by people in different places using devices that allow sounds to be sent and received. These meetings may only involve two parties, but in many cases, there are numerous parties involved.
Audioconferencing can be a solution for a number of problems that can arise when multiple parties need to meet. People who are distant and busy do not have to sacrifice the travel time since the meeting can be conducted from a nearby phone or computer. A person who would otherwise be excluded due to a bedridden illness can participate. Money that would be needed to book a meeting facility or host a lunch meeting can be saved.