Validator
A type of node responsible for determining if data submitted to the distributed ledger should be considered valid and ultimately appended to the ledger state. By exension, validators are the contributors to the consensus algorithm that ultimately governs the network.
In the context of Proof-of-Work consensus, validators are referred to as “miners” and their control is proportional to the hashrate they contribute. In Proof-of-Stake consensus validators are the nodes who have staked a sufficient amount of the prescribed tokens.
Validation
The process by which data is determined to be correct and acceptable. In the context of a distributed ledger this process consists of reconciling changes to the ledger with the current state of the ledger by multiple indepedent validator nodes according to the rules of the network’s consensus algorithm to determine if that data should be immutably appended.