ISO 17117-1:2018 defines universal and specialized characteristics of health terminological resources that make them fit for the purposes required of various applications. It refers only to terminological resources that are primarily designed to be used for clinical concept representation or to those parts of other terminological resources designed to be used for clinical concept representation. ISO 17117-1:2018 helps users to assess whether a terminology has the characteristics or provides the functions that will support their specified requirements. The focus of this document is to define characteristics and functions of terminological resources in healthcare that can be used to identify different types of them for categorization purposes. Clauses 4 and 5 support categorization according to the characteristics and functions of the terminological resources rather than the name. NOTE Categorization of healthcare terminological systems according to the name of the system might not be helpful and has caused confusion in the past. The target groups for this document are: a) organizations wishing to select terminological systems for use in healthcare information systems; b) developers of terminological systems; c) developers of terminology standards; d) those undertaking independent evaluations/academic reviews of terminological resources; e) terminology Registration Authorities. ISO 17117-1:2018 contains general characteristics and criteria with which systems can be evaluated. The following considerations are outside the scope of this document. - Evaluations of terminological resources. - Health service requirements for terminological resources and evaluation criteria based on the characteristics and functions. - The nature and quality of mappings between different terminologies. It is unlikely that a single terminology will meet all the terminology requirements of a healthcare organization: some terminology providers produce mappings to administrative or statistical classifications such as the International Classification of Diseases (ICD). The presence of such maps would be a consideration in the evaluation of the terminology. - The nature and quality of mappings between different versions of the same terminology. To support data migration and historical retrieval, terminology providers can provide maps between versions of their terminology. The presence of such maps would be a consideration in the evaluation of the terminology. - Terminology server requirements and techniques and tools for terminology developers. - Characteristics for computational biology terminology. Progress in medical science and in terminology science will necessitate updating of this document in due course.