What is a medical terminology, taxonomy, or ontology?

A medical terminology is a collection of terms that are used in the field of medicine, or in a particular sub-domain, subject, or specialty. A medical terminology can be structured in many different ways, including the following:

• A taxonomy is a controlled vocabulary that has been organized according to the hierarchical (is-a) relationships between its terms, such as that Aspirin is an antiplatelet agent. Most medical terminologies follow this organizational principle.
• A thesaurus contains additional relationships of interest between terms, such as that Aspirin may treat heart disease. A relevant example is the UMLS Metathesaurus.
• Medical ontologies are built by humans but are intended to be used computationally and thus are formally structured. For example, a medical ontology can express that a disease whose clinical course is sudden or short is equivalent to an acute disease. SNOMED CT is an example of a terminology that follows strong ontological principles.

Often, and for simplification, all structured medical terminologies are referred to as medical ontologies. Medical ontologies have been created for a variety of medical domains, such as genetics, adverse events, anatomy, drugs, diseases, and medical codes. The NCBO BioPortal is a library that contains more than 500 medical ontologies and terminologies that cover nearly 8 million medical concepts.