A hypothetical score that represents an assessment result which is entirely free of error. Sometimes true score is thought of as the average score of an infinite series of assessments with the same or exactly equivalent instruments, but with no practice effect or change in the person being assessed across the series of assessments.
Patricia Wheeler, Geneva D. Haertel, and Michael Scriven. (1992). Teacher Evaluation Glossary, Kalamazoo, MI: The Evaluation Center, Western Michigan University.