LAN & WAN.

Local Area Network & Wide Area Network

LAN

A LAN covers a small area such as one site or building, a school or a college. It interconnects a number of computers or PC's, in a limited space. It means that your information on your network or site (offices, colleges, schools) is in great security. All the computers or PC's are cabled up with LAN cables, once they're connected the files will transfer.

WAN

WAN covers a large area network that powers things like telephone wires and pylons. WAN can be used to power different cities and parts of countries, including the UK.

Why are they useful?

They are both very useful because not everywhere needs a Wide Area Network, but not everywhere needs a small Local Area Network.
What is LAN and WAN Video