Multiple forms of a test constructed to be as comparable and interchangeable as possible in their content, length, and procedures of administration, and in the scores and test properties (e.g., means, variances, and reliability indices).
Yarbrough, D. B., Shulha, L. M., Hopson, R. K., and Caruthers, F. A. (2011). The program evaluation standards: A guide for evaluators and evaluation users (3rd ed.). Thousand Oaks, CA: Sage.