Overflow answering
Overflow answering is the handling of calls a business cannot answer itself during working hours, because every line is busy or nobody picks up within a set number of rings. Those calls forward to a backup service.
Also called: overflow call handling, busy answering, no-answer forwarding
Overflow is a forwarding rule rather than a schedule. The business keeps answering its own calls; the rule only fires when a call would otherwise ring out or hit a busy tone. Typical triggers are "busy" (all lines in use) and "no answer" (unanswered after a set interval).
The backup can be an answering service, a virtual receptionist team or an AI receptionist. Because the overflow provider only sees the calls the business missed, it is a cheap way to stop losing inquiries without changing how the front desk works day to day.
Overflow answering and after-hours answering are usually bought together, since they cover the two different ways a call goes unanswered: there is nobody in, or everyone is busy.