This SAE Recommended Practice defines the principal terms and equations pertaining to automotive automatic transmission clutch plate, band, or other wet-friction systems. The terms apply directly to friction-system testing as is typically conducted on inertia-stop test equipment. Some terms can be directly applied to the analysis of friction in the transmission or brake assembly and other friction-test equipment. The glossary presents terms used to describe the set-up, testing, and results of tests as shown in Figure 1, which were taken on a clutch SAE No. 2 machine. The glossary is intended to provide a collection of definitions in the hope of eliminating confusion in terminology and a common set of terms for improving the state-of-the-art of friction-system development and their application to passenger cars and trucks. This document focuses on the terminology of friction-system testing. Reference for this type of testing are shown in Section 2.