Blockchain Beginner
A blockchain is a shared record of transactions that many computers keep in sync, rather than a single company holding the books.
Records are grouped into "blocks", and each block is cryptographically tied to the one before it — so rewriting old history would mean redoing everything since, which is effectively impossible on a large network. Because independent participants each hold a copy, no one party can quietly change the ledger.
It is the foundation under Bitcoin, Ethereum and most cryptocurrencies. Different blockchains strike different balances between decentralisation, speed and cost.
This definition is educational and not financial advice. Crypto is volatile and high-risk — always do your own research.