A computer network diagram is a schematic

Schematic

A schematic diagram represents the elements of a system using abstract, graphic symbols rather than realistic pictures. A schematic usually omits all details that are not relevant to the information the schematic is intended to convey, and may add unrealistic elements that aid comprehension...

 depicting the nodes and connections amongst nodes in a computer network

Computer network

A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....

 or, more generally, any telecommunications network

Telecommunications network

A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the terminals. Networks may use circuit switching or message switching. Each terminal in the network must have a unique address so messages or connections...

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Readily identifiable icons are used to depict common network appliances e.g. Router, and the style of lines between them indicate the type of connection. Clouds are used to represent networks external to the one pictured for the purposes of depicting connections between internal and external devices, without indicating the specifics of the outside network.