There are entire books and encyclopedic directories published by various organizations on wear/ erosion terminology. ASTM has standards for these terms (G 40 and D 4125), but there are no overarching review processes to ensure that the definitions from different organizations or societies agree. We will present our definitions. They may or may not concur with other published definitions that are based upon all of the definitions that we are aware of, our own examples of worn/ eroded surfaces, and observations in performing laboratory tribotests.