LAN: (local area network) A group of computers that share a common connection and are usually in a small area or even in the same building. For example an office or home network. They are usually connected by Ethernet cables and have high speed connections. If it was a wireless setup it would be called a WLAN, which would have a lower connection speed.
MAN: (metropolitan area network) This is a larger network that connects computer users in a particular geographic area or region. For example a large university may have a network so large that it may be classified as a MAN. The MAN network usually exist to provide connectivity to local ISPs, cable tv, or large corporations. It is far larger than a LAN and smaller than a WAN. Also large cities like London and Sydney, Australia have metropolitan area networks.
WAN: (wide area network) This is the largest network and can interconnect networks throughout the worldand is not restricted to a geographical location. The Internet is an example of a worldwide public WAN. Most WANs exist to connect LANs that are not in the same geographical area. This technology is high speed and very expensive to setup.
I hope these definitions helped as I have tried to explain LAN, WAN, and MAN in non technical terms.
Notes:
Wireless LAN is WLAN. At the moment a wired connection is still always high speed. Even though having a Wireless LAN is less mess with no cables, it compromises on speed.
With new networks popping up all the time like 3G, GSM, and GPRS, the actual end user gets to connect directly to a WMAN which was unheard of. Most of these networks are mobile data standards that previously or still are used on cell phones
you welcome :-)