Peer-to-peer refers to protocols and information transfer that take place in a decentralized way, without being mediated by a server.

At its purest, peer-to-peer file transfer uses a direct link (cable or radio) or a physical media. This is often surprisingly difficult with modern devices and operating systems, especially considering the large amounts of different protocols they support.

If there's a larger network infrastructure (be that the Internet, the telephone network, or ?snailmail), the peer-to-peer approach is not as pure, but the term may be used nevertheless. In peer-to-peer file transfer protocols, there are also often servers (called "trackers") that are needed for the peers to discover one another, but the servers are not concerned by the file transfers themselves.

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