An auto-attendant is an automated call handling system based on offering a pre-recorded menu of options to inbound callers.
Each menu option can be accepted or actioned by the pressing of a corresponding button by the caller.
A kind of “Press 3 to be connected to our marketing department” situation.
After selecting their preferred call forwarding option, the caller is connected to the relevant extension number.
Such systems perform the job of triaging incoming calls, without the staff costs of a switchboard attendant.