The purpose of this document is to a) define a set of basic concepts required to describe formal concept representation systems, especially for health sciences, b) describe representation of concepts and characteristics, for use especially in formal computer-based concept representation systems, c) describe the characteristics which synthetically describe the organisation and content of a terminological system in health, d) support the development of specific standards on categorial structures for particular healthcare subject fields with the minimum requirements to support meaningful exchange of information. This document is not suitable for, or intended for use, by individual clinicians or hospital administrators. It is not the purpose of this document to standardize the end user classification or to conflict with the concept systems embedded in national practice and languages. Topics considered outside the scope of this document include — enumeration of axiomatic concepts and semantic links, and — detailed content of health terminology systems (classifications, nomenclatures or reference terminology of health concepts).