Terminology is considered to be a subsystem which is determined semantically and functionally by a language lexicon. Terminological units have lexicon features but at the same time - their own features. The terms, belonging to a particular field, are not independent of each other, they do not represent an infinity of disparate elements but are linked by certain types of relationships (coordinated terms). Terms in a domain or subdomain belong to an organized system, structured on one or more levels with a specific hierarchy.