Generally, a peer-to-peer (or P2P) computer network is any network that does not rely on dedicated servers for communication but instead mostly uses direct connections between clients (peers). A pure peer-to-peer network does not have the notion of clients or servers, but only equal peer nodes that simultaneously function as both "clients" and "servers" to the other nodes on the network. This model of network arrangement differs from the client-server model where communication is usually relayed by the server. A typical example for a non peer-to-peer communication is email, where the email is transmitted to the server for delivery, transmitted to the destination between servers, and is fetched later by the receiving client.

A direct transmission from a client to another client is often impossible. In a peer-to-peer network, any node is able to initiate or complete any supported transaction with any other node. Peer nodes may differ in local configuration, processing speed, network bandwidth, and storage quantity. One of the first uses of the phrase "peer to peer" is in 1984, with the development of the "Advanced Peer to Peer Networking" architecture at IBM. Different peer-to-peer networks have varying P2P overlays. Note: The initialism P2P is often confused to refer to Point-to-Point, as used in telecommunications. More correctly, it should be used to refer to Peer-to-Peer connections.