Meaning 

A vocabulary control device depends on a master list of terms that can be assigned to documents. Such a master list of terms is called 'List of Subject Headings'. A list of subject headings list contains the subject access terms (preferred terms) to be used in the cataloguing or indexing operation at hand. When there are synonymous terms for a given subject, these terms are included in the list as these direct the searcher to the preferred terms for the subject. The links from non-preferred terms are called "see" references, and the links to  related terms are called "see also" references. This is accomplished through a control system, called 'subject authority system', which, for each term, documents the basis for decisions on the term and on what links connect it with other terms.