[Revised 05/16/16] A concept is a unit of thought. Chances are any biomedical concept that is represented in your data has been named by some authority. Your tax $ pay for these names to be collected, maintained, and represented in a homogeneous, tool-supported context called the UMLS (Unified Medical Language System).
The latter consists of three knowledge sources - the Metathesaurus, a Semantic Network, and a Lexicon and accompanying tools. The UMLS was created and is maintained by the U.S. National Library of Medicine (NLM), part of the National Institutes of Health (NIH). The 2016AA release of the Metathesaurus contains more than 3.25 million concepts and 13.00 million unique concept names from over 197 source vocabularies expressed using 25 different languages. Many of these vocabularies include translations into the world's major languages. Because it contains a mixture of public and proprietary content use of the UMLS requires a license, available free of charge from the NLM.
Tools are included to assist with browsing, downloading, subsetting, and representing the UMLS in existing databases. Additional tools support inter-source linking, and finding concepts in text. While not for the faint of heart, these resources are widely used around the world. Tutorial videos are available on the NLM UMLS web site.
Important, and widely used vocabularies in the UMLS include those naming diseases, lab tests, procedures, medications, chemicals, organisms, anatomic structures and genes, collected from both research and care. Several of these vocabularies are part of the standards specified for use in U.S. Electronic Health Records. Internet connectivity permitting, audience members will be challenged to "stump the Metathesaurus" - that is, name an important biomedical concept that cannot be found there. This exercise will illustrate why the UMLS should not be re-invented.