Peer-to-peer

A peer-to-peer (or "P2P") computer network exploits diverse connectivity between participants in a network and the cumulative bandwidth of network participants rather than conventional centralized resources where a relatively low number of servers provide the core value to a service or application. Peer-to-peer networks are typically used for connecting computers via largely 'ad hoc'' connections. Such networks are useful for many purposes. Sharing content files (file sharing) containing audio, video, data or anything in digital format is very common, and realtime data, such as Voice over IP traffic, is also passed using P2P technology.

The earliest peer-to-peer network in widespread use was the Usenet news server system, in which peers communicated with one another to propagate Usenet news articles over the entire Usenet network. Particularly in the earlier days of Usenet, UUCP was used to extend even beyond the Internet. However, the news server system also acted in a client-server form when individual users accessed a local news server to read and post articles.

{Wikipedia|Peer-to-peer}