1. a system for ordering test responses in a progressive series, so as to measure a trait, ability, attitude, or the like. For example, an agreement scale used on an attitude survey might have seven response options ranging from strongly disagree (1) to strongly agree (7), with neither disagree nor agree (4) as the middle point. See Likert scale; rating scale.

2. a sequence of ordered values used as a reference in measuring a physical property (e.g., weight, temperature). See interval scale; ratio scale. See also measurement level.

3. more generally, any test or other assessment instrument as a whole.