Definition: Consistency or stability of a test in producing the same or similar scores over repeated administrations.
Why it matters: Determines how much trust you can put into a score. All assessments have some error associated with them but small associated errors mean the score a student receives is a true, or reliable, measure.
Example of use: You should be able to give a test to a student in the morning and give it again to the same students in the afternoon on a different day and get similar resuts.
Salkind, N. J. (Ed.). (2008). Encyclopedia of educational psychology (Vol. 1). Sage Publications.