Specifically, it refers to the process or algorithm used to select which line will receive the call.
In the tariffs of some telephone companies, one may obtain hunting for free, but forward on busy is a charged service.
Linear hunting can also cause problems in automated equipment that answers calls, particularly if a destination extension fails on a lower-numbered line.
Circular hunting is a good way to distribute calls to electronic answering equipment such as fax machines.
[1] In most-idle hunting, calls are always delivered to whichever line has been idle the longest.