What is blockchain?
Answer
A blockchain is a distributed, decentralized digital ledger that records transactions across many computers in a way that makes the records tamper-evident and immutable. Each "block" contains a batch of transactions and a cryptographic hash of the previous block, forming a "chain." Key properties: (1) Decentralized — no single entity controls the ledger; maintained by a peer-to-peer network of nodes; (2) Immutable — once data is recorded and confirmed, it cannot be altered without altering all subsequent blocks (computationally infeasible on large networks); (3) Transparent — all transactions are visible to participants (on public blockchains); (4) Consensus-based — network participants agree on the valid state through consensus mechanisms (PoW, PoS). Originally invented by Satoshi Nakamoto for Bitcoin (2008), blockchain technology now underlies thousands of cryptocurrencies and applications beyond finance.