This International Standard defines terms used to describe the appearance of the visible surfaces of tooth flanks or the damage that can be observed on gears. For each term, a clear concise description of the relevant gear-tooth surface is given, including mention of the significant features to be observed, which can facilitate identification of the type of condition indicated. Each description of appearance constitutes a classification of a type of condition of a gear tooth or geartooth damage. Each description is accompanied by one or more illustrations to show differences which can exist with different gear tooth geometries. Comments are given with each illustration to facilitate the interpretation. This International Standard specifies only the terminology which is intended to help the recognition and reporting of the appearance and condition of gears after a period of operation. Neither causes nor preventive measures for any condition described are discussed. NOTE The English and corresponding French texts appear in adjacent columns to enable this International Standard to be used as a bilingual glossary for the appearance of gear teeth. This International Standard is arranged so that on the same page there are: • — a definition of the appearance of the gear tooth with corresponding explanations, and • — an illustration of a typical example of each with associated comments.