LAN (Local Area Network) is limited to a single site, usually an office building, while a MAN (Metropolitan Area Network) spans a small region or entire city and WAN (Wide Area Network) is not restricted to a specific geographical location. Each of the networks greatly vary in both size and infrastructure.
LANs are typically built using affordable hardware like Ethernet cables, network adapters, hubs and switches. A MAN is larger than a LAN, and may consist of smaller LANs spanning several buildings in the same town or city. A WAN is the largest, and may possibly contain several smaller LANs or MANs; it may also be limited to an organization, or publicly accessible. A good example of a global WAN is the Internet.