When you take a test or create a test, what is it that the test is designed to measure? Regardless of what the "that" may be (future performance, intelligence, aptitude, etc), it is the criterion. For example, if you are trying to predict how a person will perform in school, you may try to predict grades (the behavior) using a predictive test (such as the SAT). But does that mean that a test is valid? Hmmmm, if you are not sure, you better look up validity and reliability.