A blockchain is a ledger that records transactions in order, in batches called blocksBlockA batch of transactions added to a blockchain in one go, together with a reference to the block before it.. Each new block points back to the one before it, forming a chain all the way back to the very first transaction. Blockchains are the foundation of most cryptocurrencies, including bitcoin and ether.
How are the blocks linked?
Every block contains the HashHashA short fingerprint calculated from data, which changes completely if the data is altered by even a single character. of the previous block. A hash is a kind of fingerprint of data: change a single character and the fingerprint is completely different. If someone altered an old transaction, its block would get a new fingerprint, which would no longer match the reference in the next block. Anyone checking the chain would see at once that something was wrong.
That is why a blockchain is only ever added to, never rewritten. It works a bit like a land registry: new entries go at the end and older records stay as they are.
Who keeps the blockchain?
On open blockchains such as Bitcoin, thousands of nodesNodeA computer that runs a crypto network's software, keeps a copy of the blockchain and checks that new transactions and blocks follow the rules. each keep a copy of the whole chain. They agree on which block comes next by following fixed rules, such as proof of workProof of workA consensus method where the right to add the next block to a blockchain goes to whoever first solves a hard computing puzzle.. No single party decides what goes into the record.
Why does it matter?
A blockchain lets strangers rely on the same record without having to trust each other. The downside is that mistakes can't be corrected: crypto sent to the wrong address stays there.
Interestingly, the word "blockchain" doesn't appear anywhere in the Bitcoin whitepaper. It talks about a chain of blocks, and the name caught on later.
Everything in Myntkaup Learn is written and regularly reviewed by the Myntkaup editorial team. It is for education and is not investment advice. Editorial policy. Updated 18 October 2026.