A controlled vocabulary is a defined list of allowed terms used to index, categorize, tag, sort, and retrieve content through browsing and searching. A controlled vocabulary is
necessary to systematically organize documents, records, and content. Vocabularies range in complexity from simple lists  to the synonym rings or authority lists, to
taxonomies, classification schemes more complex thesauri and ontologies.

Source: Henderson, D., Earley, S., & Data Administration Management Association (Eds.) (2017). DAMA-DMBOK: Data management body of knowledge (Second edition). Technics Publications.