LAN, MAN, WAN
LAN (Local Area Network) - a computer network confined to a relatively small area, such as a single building or a group of adjacent buildings. A LAN can cover an entire campus, so long as the buildings are directly connected. The nodes (computers, printers, servers, etc.) are connected via bridges and routers. Devices can be connected by twisted-pair wire, coaxial cables, or fiber optic cables.
MAN (Metropolitan Area Network) - a data network designed for a town or city. In terms of geographic breadth, MANs are larger than local-area networks (LANs), but smaller than wide-area networks (WANs). Some MAN networks do without connecting media altogether, communicating instead via radio waves, using dish antenna's on rooftops.
WAN (Wide Area Network) - a computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs). Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is the Internet.