Source:http://linkedlifedata.com/resource/umls/id/C1883204
NCI: A collection of logically-related observations with a topic-specific commonality about the subjects in a trial, used in the regulatory submission process. The logic of the relationship may relate to the scientific subject matter of the data, or to its role in the trial. Typically, each domain is represented by a dataset, but it is possible to have information relevant to the same topicality spread among multiple datasets. (CDISC Glossary)