A wide area network, or WAN, is a network that connects computers and resources over a geographical area.
This contrasts with a local area network (LAN), which connects computers which are close to each other: for example, within a single premises. A WAN connects several of these smaller networks into a larger overall network.
In business terms, they are used to relay data across the different branches of an organisation. They can provide the benefits of increased security and customisation.