Touch-tone IVR
A classic IVR plays a recorded announcement and asks callers to choose with their keypad: "Press 1 for sales, 2 for support." The caller works through the menu and ends up in a queue or on an extension. It can also read out stored information such as a balance or opening hours.
Its strength is simplicity: with few options it is quick and predictable. Its weakness is that it doesn't understand what the caller wants; a request that isn't in the menu has no key, and the work usually still falls to an agent.