The decentralized interactions between parties in a distributed network, partitioning tasks or workloads between peers.
Peer-to-peer (P2P) refers to a distributed network where “computer systems” communicate with each other to share data or tasks. This means that two or more parties arranging and agreeing to deal with each other are sufficient for the whole process to occur. Furthermore, a central server isn’t required to facilitate and manage such communication.
All peers are considered equal and enjoy the same privileges. The only requirement to access a P2P system is an internet connection and a copy of the software (or protocol) used. Peers or nodes generally make all or some parts of their resources available to the network in the absence of a central server processing request and managing resources/tasks.
P2P has special significance in the context of cryptocurrencies and blockchain. For instance, Bitcoin’s whitepaper defines its protocol as “A Peer-to-Peer Electronic Cash System” — a reference to the mutually beneficial and equal involvement of all participants without the need for any intermediaries. All peers or nodes of a blockchain typically have the same copy of records of accounts and transactions history, although miners (and other “full nodes”) who contribute processing power to the network in lieu of block subsidies and transaction fees have a more complete copy of the records.
Bitcoin is a true peer-to-peer protocol which doesn’t rely on any third party with centralized control, but P2P doesn’t always have to be blockchain-based. BitTorrent was originally not blockchain-based (before Tron acquisition), yet it is considered one of the largest decentralized peer-to-peer systems.