Consensus

The mechanism by which a blockchain agrees on the canonical state across all nodes.

Consensus is how distributed nodes in a blockchain agree on which transactions happened and in what order. Proof of work (Bitcoin) makes nodes compete with computational power. Proof of stake (Ethereum, Solana, Cosmos chains) requires validators to lock tokens as collateral, with slashing for misbehavior.

Consensus algorithms have different finality guarantees. Bitcoin's PoW finality is probabilistic — after 6 confirmations, reversal is practically impossible. Tendermint-style BFT consensus offers instant finality at the cost of validator-set centralization. The right choice depends on what the chain is optimizing for.