A standardized test is a test that is administered and scored in a consistent, or "standard", manner. Standardized tests are designed in such a way that the questions and interpretations are consistent and are administered and scored in a predetermined, standard manner.

Any test in which the same test is given in the same manner to all test takers, and graded in the same manner for everyone, is a standardized test. Standardized tests do not need to be high-stakes tests, time-limited tests, or multiple-choice tests. A standardized test may be any type of test: a written test, an oral test, or a practical skills performance test. The questions can be simple or complex. The subject matter among school-age students is frequently academic skills, but a standardized test can be given on nearly any topic, including driving tests, creativity, athleticism, personality, professional ethics, or other attributes.

The opposite of standardized testing is non-standardized testing, in which either significantly different tests are given to different test takers, or the same test is assigned under significantly different conditions (e.g., one group is permitted far less time to complete the test than the next group) or evaluated differently (e.g., the same answer is counted right for one student, but wrong for another student).

Most everyday quizzes and tests taken by students during school meet the definition of a standardized test: everyone in the class takes the same test, at the same time, under the same circumstances, and all of the students are graded by their teacher in the same way. However, the term standardized test is most commonly used to refer to tests that are given to larger groups, such as a test taken by all adults who wish to acquire a license to have a particular kind of job, or by all students of a certain age. Most standardized tests are forms of summative assessments - assessments that attempt to measure the learning of the participants at the end of an instructional unit.

Because everyone gets the same test and the same grading system, standardized tests are often perceived as being fairer than non-standardized tests. Such tests are often thought of as fairer and more objective than a system in which some students get an easier test and others get a more difficult test. Standardized tests are designed to permit reliable comparison of outcomes across all test takers, because everyone is taking the same test. However, both testing in general and standardized testing in specific are criticized by some people. For example, some people believe that it is unfair to ask all students the same questions, if some students' schools did not have the same learning standards.