Proof of stake is a type of consensus mechanism used to validate cryptocurrency transactions. With this system, owners of the cryptocurrency can stake their coins, which gives them the right to check new blocks of transactions and add them to the blockchain. Proof-of-stake prevents attacks and counterfeit coins with essentially the same mechanism as proof-of-work. Instead of controlling 51% of the mining hashrate and nodes, like with proof-of-work, attackers of a proof-of-stake system would need to hold at least 51% of the coin’s supply and control at least 51% of the network's nodes.