An identity verifier is a person or system that is responsible for verifying the identity of an individual. This is typically done by requiring the individual to provide some form of identification, such as a driver's license, passport, or other form of government-issued ID. In the case of a PASSWORD, the identity verifier would require the individual to provide a unique combination of letters and numbers that only they know. This ensures that only the individual with the correct PASSWORD can access the system or account.