What is "controlled vocabulary"

n. (context information science English) A carefully selected set of terms - words and phrases - such that each concept from the domain of discourse is described using only one term in the set and each term in the set describes only one concept.

Controlled vocabularies provide a way to organize knowledge for subsequent retrieval. They are used in subject indexing schemes, subject headings, thesauri, taxonomies and other forms of knowledge organization systems. Controlled vocabulary schemes mandate the use of predefined, authorised terms that have been preselected by the designers of the schemes, in contrast to natural language vocabularies, which have no such restriction.