Test difficulty refers to how challenging a test is for the individuals taking it. This can depend on various factors, including the complexity of the questions, the level of knowledge required, and the test-taker's familiarity with the subject matter. For example, a math test may be considered difficult if it includes advanced concepts that students have not yet mastered. Additionally, test difficulty can vary based on the format of the test. Multiple-choice questions may be easier for some, while open-ended questions might require deeper understanding and critical thinking. Overall, understanding test difficulty helps educators design assessments that accurately measure student learning and skills.