A computer network is two or more computers connected together. Computers in a network can communicate with each other.
A computer needs some sort of hardware to connect to a network, e.g. a network interface card, or a modem. There are two types of computer network:
Local Area Networks (LANs): computers connected over a relatively small distance, usually one building or one site.
Wide Area Networks (WANs): computers connected together over larger distances, such as all branches of a company. The Internet is a WAN.
Computers on a network are called terminals.