Is a consensus where validation occurs through signing blocks with a wallet (or delegated key of the wallet) on which a definite sum of tokens is blocked.
Unlike Proof of Work (PoW), PoS doesn’t depend on hash algorithms. To confirm ownership of funds (coins or tokens) digital signature is used. Every participant has a chance to be randomly chosen as new Block creator (validator) and this chance can be increased proportionally by increasing the “weight” of the node (it’s shared in the total pool of locked m-tokens). In this case consensus is something like lottery. Reward is calculated in coins.
Proof of Service is a part of node verification based on Proof of Stake (PoS) before engaging in the network. It is an additional condition to PoS, which shows that node provides some service.