A blockchain is a shared record that many computers keep in sync. Nobody owns it and nobody can quietly change history.
The pieces
- Block: a batch of transactions with a timestamp.
- Chain: each block includes a fingerprint (a hash) of the previous block, linking them together.
- Nodes: computers that store a copy of the chain and check new blocks.
- Consensus: the rule nodes use to agree on the next block, for example proof of work (mining) or proof of stake.
Why it is hard to alter
If someone changed an old block, its fingerprint would change, breaking the link to every later block. Honest nodes would reject the altered chain.
A simple example
Imagine a village notebook that everyone copies. When a trade happens, a page is added and every villager adds it to their copy. To cheat, you would need to change most notebooks at the same time.
What it does not guarantee
A blockchain proves that a record was not altered. It does not prove an app, coin or project is honest. Learn how mining works in how Bitcoin mining works, and how coins differ in the basics guide.