Proof of Stake (PoS)
Plain English
Instead of miners using electricity, validators are chosen to create blocks based on how many coins they "stake" (lock up). More stake = higher chance of being chosen. Much more energy efficient than Proof of Work. Solana uses a variation of this.
Technical
Consensus mechanism where validators are selected to produce blocks proportionally to their staked tokens rather than computational power. Validators risk losing staked capital (slashing) for malicious behavior. Dramatically reduces energy consumption compared to PoW while maintaining security through economic incentives. Ethereum 2.0, Solana, and Cardano use PoS variants.