What is the consensus mechanism in cryptocurrencies?

The consensus mechanism in cryptocurrencies is the process during which a group of identical nodes determines the validity of transactions on the blockchain. Consensus mechanisms are methods that are used to reach a single decision. These sets of rules and techniques help protect the network from hacker attacks. There are different consensus mechanisms with different scalability, power consumption, and security level. The methods are used in different blockchains, but the goal of any of them is to ensure the validity of transactions.