Proof of Stake (PoS)
Proof of Stake selects block producers based on the coins they have locked up ("staked") rather than computing power.
In depth
Validators deposit coins as collateral; the protocol picks one to propose each block, weighted by stake, and others attest to it. Misbehaviour is punished by "slashing" part of the deposit, so honesty is the profitable strategy. Ethereum switched from PoW to PoS in 2022, cutting its energy use by over 99%.
Why it matters
PoS underpins most modern chains and is what makes staking rewards possible.