Consensus Mechanism
The rules a blockchain network uses to agree on the valid state of the ledger.
A consensus mechanism is the protocol by which distributed nodes reach agreement on which transactions are valid and in what order they occurred — without trusting a central authority.
The two dominant mechanisms are Proof of Work (PoW), used by Bitcoin, where miners expend computational energy to propose blocks, and Proof of Stake (PoS), used by Ethereum and most modern chains, where validators lock up ('stake') tokens as collateral and are selected to propose blocks proportionally.
Other variants include Delegated Proof of Stake (DPoS), Proof of History (Solana), and Byzantine Fault Tolerant (BFT) algorithms. Each involves trade-offs between security, speed, decentralisation, and energy use.