eneral, the term network can refer to any interconnected group or system. More specifically, a network is any method of sharing information between two systems (human or mechanical). It can also mean (see wordnet.princeton.edu/perl/webwn):

• An interconnected system of things or people; "he owned a network of shops"; "retirement meant dropping out of a whole network of people who had ...
• (broadcasting) A communication system consisting of a group of broadcasting stations that all transmit the same programs; "the networks compete to broadcast important sports events"
• (from net) An open fabric of string or rope or wire woven together at regular intervals
• A system of intersecting lines or channels; "a railroad network"; "a network of canals"
• Communication with and within a group; "You have to network if you want to get a good job"
• (electronics) A system of interconnected electronic components or circuits