Test-Retest Reliability is a measure used to assess the consistency of a test or measurement over time. It involves administering the same test to the same group of people on two different occasions. If the results are similar, the test is considered reliable. This type of reliability is important in fields like psychology and education, where accurate measurements are crucial. High test-retest reliability indicates that the test produces stable results, while low reliability suggests that the test may be influenced by external factors or inconsistencies in the measurement process.