Hunt Group and Queues are methods of distributing phone calls between users and agents based on predetermined rules. Queues and Hunt Groups usually parallel certain departments. For example technical support will have it's own Hunt group and the sales department will have its own Queue.
After agents are assigned to Hunt Groups calls are routed to them in either random or a predetermined order. If a call is not answered the system will "hunt" out the next available agent. If that agent is also busy, the call will go to the next one in line until it is answered.
Hunt groups can also be defined to have all relevant group extensions ring at once, allowing for the first agent the pick up his phone to receive the call. If despite all "hunting" a call is not answered it can be routed to a special group mailbox.
Queues are essentially more sophisticated Hunt Groups that use ACD - Automatic Call Distribution rules to route calls to appropriate departments and manage the on-hold experience of customers. Queues help minimize on missed calls and voicemails.
As implied by the name, calls are not just routed between agents but, if needed, can also be queued up for certain agents or for an entire department, allowing for handling of a much larger call volume with a limited staff.
Callers also receive a more engaging experience with the system providing queue information and hold time estimates, directional prompts, on-hold music, and business and promotional information.
The main difference from Hunt groups is that agents in queues have priority ranking and the ACD will route calls to them based on those ranking and not only by mere availability or predetermined order. Agents can log themselves out from a queue so their priority is not considered by the ACD. The ACD is also aware when agents are already on calls and only routes to available staff, making the distribution process much more efficient than in Hunt groups.
Another advantage is that ACD can route calls between different departments (queues) and can also send a caller back to the auto attendant.