What Is a Blockchain?

A blockchain is a shared record that many computers keep in sync. New entries are grouped into blocks, checked against the rules, and then added in order.

What makes it different from a normal database is the way history is linked. Each new block points back to the one before it.

This structure does not make a blockchain magical or always better. It makes it useful when many parties need a shared history without trusting one company to edit the ledger.

Bitcoin uses this for money. Ethereum uses the same idea for money plus application state. The next question is how networks agree on new blocks.