A record of transactions kept by many computers at once instead of one company or bank, so no single party can quietly rewrite it.
A blockchain stores data in “blocks,” each one linked to the one before it, forming a chain. Every participating computer (a “node”) holds a copy, and adding a new block requires the network to agree it’s valid, which is what makes the record hard to alter after the fact. No central administrator can edit the ledger unilaterally.
This is the infrastructure underneath every cryptocurrency — Bitcoin, Ethereum, Solana — but the technology itself is general-purpose: it’s a way of maintaining a trustworthy shared record without a trusted middleman.
The idea traces to a single nine-page document that solved a specific problem no one had cracked before: how to stop the same digital coin being spent twice without a bank in the middle to check.
Source: Nakamoto, S. (2008), “Bitcoin: A Peer-to-Peer Electronic Cash System.”