This part of ISO 6621 defines the most commonly used terms for piston rings. These terms designate either types of piston rings or certain characteristics and phenomena of piston rings. The terms and definitions in this part of ISO 6621 apply to piston rings for reciprocating internal combustion engines. They may also be used for piston rings of compressors working under analogous conditions. NOTE 1 Further terms and definitions covering measuring principles are given in ISO 6621-2. NOTE 2 In addition to terms given in the three official ISO languages (English, French and Russian), this part of ISO 6621 gives the equivalent terms in the German, Spanish, Portuguese, Italian and Japanese languages. However, only the terms given in the official languages can be considered as ISO terms. These have been included at the request of Technical Committee ISO/TC 22 and are published under the responsibility of the member bodies for Germany (DIN), Spain (AENOR), Portugal (IPQ), Italy (UNI) and Japan (JIS).