Validators, much like miners in a Proof-of-Work(PoW) network, are network nodes that operate in Proof of Stake (PoS) blockchains, also validating transaction blocks to the blockchain.
Validators are generally picked at random, based on the amount of cryptocurrency they are willing to stake or lock up in a smart contract, to win the rights to validation.
This is different than the competition-style mechanism like Proof-of-Work (PoW)
As transactions occur, validators batch individual transactions into a block and then verify it.
The number of transactions per block is designated by each blockchain’s rules, and each blockchain decides how many other validators are needed to agree to the valid transactions before the block is closed.
But once the block has been completed, the validators process the block and permanently add the new record to the blockchain.
Validators can lose some or all of their stake if they validate bad data.
For their work, validators are paid transaction fees by the sender of the transaction.