Consensus Mechanism
The rulebook a decentralised network uses to agree on one shared version of history.
A consensus mechanism is how thousands of independent computers, some of which may be faulty or hostile, settle on the same ledger. It defines who gets to add the next block, how competing chains are resolved and what happens to bad actors.
Proof of work and proof of stake are the two dominant families, but delegated proof of stake, proof of authority and Byzantine fault tolerant designs are also in production use.