Wide Area Telephone Service

Wide Area Telephone Service (WATS) was a flat-rate long-distance service for customer dial-type telecommunications in the service areas of the North American Numbering Plan (NANP). The service was between a given customer phone (also known as a "station") and stations within specified geographic rate areas, employing a single telephone line between the customer location and the serving central office.

Source: Wikipedia — Wide Area Telephone Service (CC BY-SA 4.0)