PoW : Proof of work is a protocol that has the main goal of deterring cyber-attacks such as a distributed denial-of-service attack (DDoS) which has the purpose of exhausting the resources of a computer system by sending multiple fake requests. The Proof of work concept existed even before bitcoin, but Satoshi Nakamoto applied this technique to his/her – we still don’t know who Nakamoto really is – digital currency revolutionizing the way traditional transactions are set.
PoS : Proof of stake is a different way to validate transactions based and achieve the distributed consensus. It is still an algorithm, and the purpose is the same of the proof of work, but the process to reach the goal is quite different.