Abstract： The terminology related to the hydatid cyst is sometimes inappropriate and wrong designations are used, based on incorrect concepts. "Hydatid cyst" is the larval form of the tapeworms of the genus Echinococcus granulosus, a parasite found in the small intestine of carnivores. The disease, called cystic echinococcosis, is among the most neglected parasitic diseases despite the development of new drugs and other treatment modalities. Although all of us know the vital cycle of the parasite and the different aspects of the disease, the designations around the parasite, its evolution and some therapeutic procedures are not uniform. It would be useful, for all of us, to use the same nomenclature and it is absolutely necessary that the nomenclature is correct and universally accepted. In this paper I remember the correct terms related to all aspects of the hydatid cyst's nomenclature, including especially the anatomical and surgical terminology, as well as the criteria to define the cyst inactivity and the way to know when the cyst range the inactive stage after therapy.