What do we call a network whose elements may be separated by some distance? It usually involves two or more small networks and dedicated high-speed telephone lines.

A Wide Area Network (WAN) is a network that covers a large geographic area, connecting multiple smaller networks (LANs) over long distances. WANs typically use dedicated high-speed communication lines (like fiber optics, leased lines, or satellite links) provided by telecom carriers to connect networks in different cities, countries, or continents. The definition in the question precisely matches WAN characteristics.