1. WAN is short for wide area network. They are used when the computers that need to be connected together are in different places.
2. Like LANs, WANs need servers to opperate the network, but users connect up to the network using modems, usualy connected to the telephone system. Wireless technology such as microwaves or satelite can also be used - but this is very expensive.
3. WANs are used by companies who have employees working away from the firm's main sites. A good example would be oil exploration engineers who work in remote parts of the world. They are also used by firms who have a lot of teleworkers.