Quick Definition
A peer-to-peer (P2P) network is a decentralized communication model in which every participant (or “peer”) can connect, share data, and relay messages directly with every other participant, no central server or coordinator required.

Key Takeaways

• Decentralized architecture: The network has no single point of control or failure; each peer performs both client and server-like functions.
• Equal peers: Every node can originate, validate, and forward data, making the system inherently democratic.
• Fault & censorship-resistant: If some peers go offline or are blocked, the rest continue operating and propagating data.
• Resource sharing: Bandwidth, storage, and processing load are distributed across the network, improving scalability.
• Foundational to Bitcoin: Bitcoin’s nodes use a P2P overlay to broadcast transactions and blocks, enforce consensus rules, and keep the ledger globally synchronized.

In-Depth Explanation

Traditional client-server systems rely on a hub (the server) to route all traffic. In contrast, a P2P network forms a mesh overlay: peers discover one another (via mechanisms like DNS seeds or gossip), open direct encrypted connections, and exchange information. When a peer wants to share data, it broadcasts it to its neighbors; those neighbors verify the data and relay it onward until it reaches the entire network.

Because no single entity dictates what data is “valid,” every peer must run the same protocol rules and independently verify that incoming messages conform. This self-validation is what gives P2P systems their robustness and trust-minimizing qualities. If a malicious or malfunctioning peer tries to propagate invalid data, honest peers simply refuse to forward it.

Bitcoin example:

1. Transaction propagation: Wallet software signs a transaction and broadcasts it to nodes.
2. Flood relay: Those nodes validate the transaction (checking signatures, inputs, fees) and “gossip” it to their peers, rapidly spreading it worldwide.
3. Block distribution & consensus enforcement: When a miner finds a valid block, it floods the block the same way. Each full node verifies the block’s proof-of-work and every transaction before accepting it and building on top.

Other well-known P2P systems include BitTorrent (file sharing), Tor (onion routing), and IPFS (content-addressed storage). Across all these examples, the defining trait is the absence of a central choke point.