The set of rules by which all nodes in a blockchain agree, without any central administrator, on what the next block looks like and which transactions are valid. It's the core that lets a decentralized network operate securely and resist fraud; the two most common are Proof of Work (PoW) and Proof of Stake (PoS).

A mathematical function that turns input data of any length into a fixed-length, gibberish-looking digital fingerprint. Its key properties: the same input always gives the same output, a tiny change in input yields a wildly different output, and it's practically impossible to reverse the output back to the original input. It's the basic tool that links blocks and makes data tamper-evident on a blockchain.