A blockchain is a distributed ledger technology that records transactions across multiple computers so that the record cannot be altered retroactively. Each block in the chain contains a cryptographic hash of the previous block, a timestamp, and transaction data. This structure makes blockchains inherently resistant to modification of data.
The decentralized nature of a blockchain means no single entity controls the entire chain. Validators or miners across the network maintain consensus on the state of the ledger through various mechanisms such as Proof of Work or Proof of Stake. This decentralization provides resilience against censorship and single points of failure.
Blockchains power cryptocurrencies like Bitcoin and Ethereum, but their applications extend far beyond digital currency. Smart contracts, NFTs, decentralized applications, and supply chain tracking are just a few of the use cases that leverage blockchain immutability and transparency.