TL;DR
Proof of Stake is a consensus mechanism where validators stake cryptocurrency as collateral to participate in block production, replacing the energy-intensive mining of Proof of Work.
In Proof of Stake, validators lock up (“stake”) tokens as collateral. The protocol selects validators to produce blocks based on their stake amount — more stake means higher probability of selection. If a validator acts maliciously (like trying to approve invalid transactions), their stake can be slashed (partially destroyed). This economic incentive aligns validators with honest behavior.
Solana combines Proof of Stake with Proof of History (PoH) for its consensus. PoH provides a cryptographic clock that timestamps transactions before consensus, allowing validators to agree on transaction order without extensive back-and-forth communication. This is how Solana achieves 400ms block times and high throughput. Validators stake SOL and participate in Tower BFT consensus to finalize blocks.
Bitcoin’s Proof of Work requires miners to solve computational puzzles, consuming massive energy. PoS replaces this with economic commitment (staking). Advantages: ~99.9% less energy use, lower barrier to participation, and the ability to penalize bad actors (slashing). Disadvantages: potential centralization if large holders dominate staking, and the “nothing at stake” problem (addressed by slashing mechanisms).