Recommendation ITU-T G.870/Y.1352 provides terms, definitions and abbreviations used in optical transport network (OTN) Recommendations. In this edition, Recommendations (namely Source Recommendation per term) are identified that originally introduced OTN terms and are primary responsible for the definitions of those terms. For the OTN terms defined in the previous edition, this edition provides the pointers to the Sources Recommendations as a directory. Official definitions are now given in those Source Recommendations.