Wikipedia
Proof-of-stake (PoS) is a method by which a cryptocurrency blockchain network aims to achieve distributed consensus. While the proof-of-work (PoW) method asks users to repeatedly run hashing algorithms or other client puzzles to validate electronic transactions, proof-of-stake asks users to prove ownership of a certain amount of currency (their "stake" in the currency). Peercoin was the first cryptocurrency to launch using proof-of-Stake. Other prominent implementations are found in BitShares, ShadowCash, Nxt, BlackCoin, NuShares/NuBits, Qora and Nav Coin. Ethereum has planned a hard fork transition from PoW to PoS consensus. Both Peercoin and Decred hybridize PoW with PoS and combine elements of both consensus approaches in an attempt to garner the benefits of the two systems and create a more robust notion of consensus.