Blockchain
A blockchain is a shared record of transactions kept as a chain of blocks. Each block is linked to the previous one by a hash, so rewriting history is practically impossible.
How it works
Copies of the blockchain are kept by thousands of network participants (nodes), not on one server. New transactions are grouped into a block, participants check them against shared rules and add the block to the end of the chain. Which block gets accepted is decided by a consensus mechanism: Proof of Work (mining) or Proof of Stake (staking).
A hash is a short fingerprint of data: change one character in a block and the hash becomes completely different. Each block contains the hash of the previous one, so faking an old record breaks every block after it, and honest nodes reject it.
A public blockchain is open: anyone can look up transactions in a block explorer. Some blockchains, such as Ethereum, can run programs called smart contracts, which power DeFi, NFTs and tokens.
You send a friend 100 USDT. The transaction goes into the mempool (the waiting line), then into a block. After that anyone can look it up in a block explorer by its transaction hash and see the amount, addresses and time.
On bitcoin a new block appears about every 10 minutes. To rewrite a transaction from an hour ago, an attacker would have to redo about 6 blocks faster than the rest of the network, which takes enormous computing power.
A common mistake is assuming the blockchain makes everything around it safe. It only protects records inside the network. If you send coins to the wrong address or to a scammer, the blockchain records that faithfully and nobody can reverse it. Check the address and network before sending, and for a large amount do a small test transfer first.
Questions and answers
What is a blockchain in simple terms?
It is a shared notebook of records that thousands of participants keep a copy of. New pages are added by common rules, and old ones are almost impossible to change.
Can a blockchain be hacked?
Attacking a large network itself is extremely costly and hard. What usually gets hacked is what surrounds it: exchanges, wallets, buggy smart contracts and people through phishing.
How is a blockchain different from a normal database?
A normal database is run by one company that can edit records. A blockchain is kept by many independent participants, and records cannot be quietly changed after the fact.
Related terms
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Updated: 2026-10-19