Proof of Stake (PoS) is a consensus mechanism used in blockchain networks to validate transactions and create new blocks. Unlike Proof of Work, which requires miners to solve complex mathematical problems, PoS allows validators to create new blocks based on the number of coins they hold and are willing to "stake" as collateral. This method is more energy-efficient and reduces the need for extensive computational power. In a PoS system, the likelihood of being chosen to validate a block is proportional to the amount of cryptocurrency staked. This encourages users to hold and invest in their coins, promoting network security and stability. PoS is used by various cryptocurrencies, including Ethereum after its transition from PoW.