WAN – Wide Area Network
WAN spans a large physical distance. It is a geographically a dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.
A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by anyone organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and SONET/SDH for connectivity over longer distances.