Blockchain
A distributed, immutable digital ledger that records transactions across a network of computers without a central authority.
What is Blockchain?
A blockchain is a type of distributed ledger technology (DLT) in which data is stored in linked blocks — each containing a cryptographic hash of the previous block, a timestamp, and transaction data. Once recorded, data in any given block cannot be altered retroactively without altering all subsequent blocks and gaining consensus from the majority of the network. This design makes blockchains resistant to modification and fraud without a central administrator. Blockchains are maintained by a peer-to-peer network using consensus mechanisms such as Proof of Work (Bitcoin) or Proof of Stake (Ethereum). While blockchain underpins cryptocurrencies, the technology has broader applications in supply chain tracking, digital identity, smart contracts, and financial settlements.
Example
Bitcoin's blockchain records every transaction ever made since 2009 in a public, permanent ledger. When Alice sends 0.1 BTC to Bob, the transaction is broadcast to the network, verified by miners competing to solve a mathematical puzzle (Proof of Work), and added to a block that is cryptographically linked to all prior blocks — making the history essentially tamper-proof without control of more than half the network's computing power.