A computer network is a digital telecommunications network for sharing resources between nodes, which are computing devices that use a common telecommunications technology. Data transmission between nodes is supported over data links consisting of physical cable media, such as twisted pair or fiber-optic cables, or by wireless methods, such as Wi-Fi, microwave transmission, or free-space optical communication.
Network nodes are network computer devices that originate, route and terminate data communication. They are generally identified by network addresses, and can include hosts such as personal computers, phones, and servers, as well as networking hardware such as routers and switches. Two such devices can be said to be networked when one device is able to exchange information with the other device, whether or not they have a direct connection to each other. In most cases, application-specific communications protocols are layered (i.e. carried as payload) over other more general communications protocols.
Computer networks support many applications and services, such as access to the World Wide Web, digital video, digital audio, shared use of application and storage servers, printers, and fax machines, and use of email and instant messaging applications. Computer networks may be classified by many criteria, for example, the transmission medium used to carry their signals, bandwidth, communications protocols to organize network traffic, the network's size, topology, traffic control mechanism, and organizational intent. The best-known computer network is the Internet. Source Wikipedia