WAN stands for wide area network.
Wide area network are the networks that spread across the countries.
Basically a wide area network (WAN) is a group of computers that are separated by large distances and tied together.
Wide area network can be a group of local area networks that are spread across several locations and connected together to look like on big LAN which is then called as WAN.
The WANs link computers to facilitate fast and efficient exchange of information at lesser costs and higher speeds.
Computers that are connected to a wide area network are sometime connected through public networks such as telephone system. Sometimes they can also be connected through leased lines or satellites.
The largest wide area network (WAN) in existence is the Internet.