Glossary
Consensus mechanism
The rule a distributed blockchain uses to agree on which transactions are valid and in what order, without trusting any single party.
A consensus mechanism is how a permissionless network of nodes agrees on a single, ordered history of transactions when no central authority is in charge. Two designs dominate.
Proof of Work (PoW), used by Bitcoin, has miners race to find a number whose hash meets a difficulty target. The first to find one publishes the next block; rivals re-converge on the longest chain. PoW pays for security in electricity — an attacker has to outspend the rest of the network in real-world energy.
Proof of Stake (PoS), used by Ethereum since 2022 and most newer chains, has validators put up a deposit ("stake") and take turns proposing blocks. Cheat and your stake gets slashed. PoS pays for security in opportunity cost — an attacker has to acquire and risk a majority of the staked token.
Both produce probabilistic finality: a block becomes harder to reverse the more blocks pile on top of it. Neither is "better"; they make different trade-offs around energy use, hardware barriers, and the economics of who ends up running the network.