Source: ANSI/NISO Z39.19 - Guidelines for the Construction, Format, and Management of Monolingual Controlled Vocabularies (2005) ISBN: 1-880124-65-3 is p. 157-167.

associative relationshipA relationship between or among terms in a controlled vocabulary that leads from one term to other terms that are related to or associated with it; begins with the words SEE ALSO or related term (RT).
authority fileA set of established headings and the cross-references to be made to and from each heading, often citing the authority for the preferred form or variants. Types of authority files include name authority files and subject authority files.
broader termA term to which another term or multiple terms are subordinate in a hierarchy. In thesauri, the relationship indicator for this type of term is BT.
browsingThe process of visually scanning through organized collections of representations of content objects, controlled vocabulary terms, hierarchies, taxonomies, thesauri, etc.
candidate termA term under consideration for admission into a controlled vocabulary because of its potential usefulness. Also known as provisional term.
classification schemeA method of organization according to a set of pre-established principles, usually characterized by a notation system and a hierarchical structure of relationships among the entities.
compound termA term consisting of more than one word that represents a single concept. Compound terms must be constructed according to the guidelines of this Standard.

See also bound term (in the glossary) and precoordination.
conceptA unit of thought, formed by mentally combining some or all of the characteristics of a concrete or abstract, real or imaginary object. Concepts exist in the mind as abstract entities independent of terms used to express them.
controlled vocabularyA list of terms that have been enumerated explicitly. This list is controlled by and is available from a controlled vocabulary registration authority. All terms in a controlled vocabulary must have an unambiguous, non-redundant definition.

NOTE: This is a design goal that may not be true in practice; it depends on how strict the controlled vocabulary registration authority is regarding registration of terms into a controlled vocabulary.

At a minimum, the following two rules must be enforced:

1. If the same term is commonly used to mean different concepts, then its name is explicitly qualified to resolve this ambiguity. NOTE: This rule does not apply to synonym rings.

2. If multiple terms are used to mean the same thing, one of the terms is identified as the preferred term in the controlled vocabulary and the other terms are listed as synonyms or aliases.
cross-referenceA direction from one term to another. See associative relationship; equivalence relationship; hierarchical relationship.
descriptorSee preferred term.
document Any item, printed or otherwise, that is amenable to cataloging and indexing. The term applies not only to written and printed materials in paper or microform versions (e.g., books, journals, maps, diagrams), but also to non-print media (e.g., machine-readable records, transparencies, audiotapes, videotapes) and, by extension, to three-dimensional objects or realia (e.g., museum objects and specimens). A document is a content object.
entry termThe non-preferred term in a cross reference that leads to a term in a controlled vocabulary. Also known as "lead-in term.” In thesauri, the relationship indicator for this type of term is U (USE); its reciprocal is UF (USED FOR). See also preferred term.
headingA preferred name or term. Types of headings include proper name headings (which can be called identifiers), subject headings, and terms. A heading may include a qualifier.
hierarchical relationshipA relationship between or among terms in a controlled vocabulary that depicts broader (generic) to narrower (specific) or whole-part relationships; begins with the words broader term (BT), or narrower term (NT).
hierarchyBroader (generic) to narrower (specific) or whole-part relationships, which are generally indicated in a controlled vocabulary through codes or indentation. See also broader term; narrower term.
homographOne of two or more words that have the same spelling, but different meanings and origins. In controlled vocabularies, homographs are generally distinguished by qualifiers.
indexingA method by which terms or subject headings from a controlled vocabulary are selected by a human or computer to represent the concepts in or attributes of a content object. The terms may or may not occur in the content object.
indexing languageA controlled vocabulary or classification system and the rules for its application. An indexing language is used for the representation of concepts dealt with in documents [content objects] and for the retrieval of such documents [content objects] from an information storage and retrieval system. [ISO 5127/1]
indexing termThe representation of a concept in an indexing language, generally in the form of a noun or noun phrase. Terms, subject headings, and heading-subheading combinations are examples of indexing terms. Also called descriptor.
keywordA word occurring in the natural language of a document that is considered significant for indexing and retrieval.
narrower termA term that is subordinate to another term or to multiple terms in a hierarchy. In thesauri, the relationship indicator for this type of term is NT.
natural languageA language used by human beings for verbal communication. Words extracted from natural language texts for indexing purposes without vocabulary control are often called keywords.
navigationThe process of moving through a controlled vocabulary or an information space via some pre-established links or relationships.
near synonymA term whose meaning is not exactly synonymous with that of another term, yet which may nevertheless be treated as its equivalent in a controlled vocabulary.
node labelA “dummy” term, often a phrase, that is not assigned to documents when indexing, but which is inserted into the hierarchical section of some controlled vocabularies to indicate the logical basis on which a class has been divided. Node labels may also be used to group categories of related terms in the alphabetic section of a controlled vocabulary.
non-preferred termSee entry term. See also preferred term.
permuted displayA type of index where individual words of a term are rotated to bring each word of the term into alphabetical order in the term list. See also KWIC and KWOC (in the glossary).
pick listA graphical user interface device that allows the user to select from a pre-set list of terms. Typically the list of terms is shown when the user clicks on a down arrow next to the entry box for the term.
postcoordinationThe combining of terms at the searching stage rather than at the subject heading list construction stage or indexing stage. See also precoordination.
precoordination The formulation of a multiword heading or the linking of a heading and subheadings to create a formally controlled, multi-element expression of a concept or object. Precoordination is often used to ensure logical sorting of related expressions.

See also postcoordination.
preferred term One of two or more synonyms or lexical variants selected as a term for inclusion in a controlled vocabulary. See also nonpreferred term. NOTE: In the previous version of this Standard, a preferred term was known as a descriptor.
provisional termSee candidate term.
qualifierA defining term, used in a controlled vocabulary to distinguish homographs. A qualifier is considered part of a term, subject heading, or entry term, but is separated from it by punctuation. The qualifier is generally enclosed in parentheses.
quasi-synonymSee near synonym.
reciprocity Semantic relationships in controlled vocabularies must be reciprocal, that is each relationship from one term to another must also be represented by a reciprocal relationship in the other direction. Reciprocal relationships may be symmetric, e.g. RT / RT, or asymmetric e.g. BT / NT. See also asymmetric and symmetric.
related termA term that is associatively but not hierarchically linked to another term in a controlled vocabulary. In thesauri, the relationship indicator for this type of term is RT.
relationship indicatorA word, phrase, abbreviation, or symbol used in thesauri to identify a semantic relationship between terms.
scope noteA note following a term explaining its coverage, specialized usage, or rules for assigning it.
siblingA term that shares the same broader term (one level higher) as other terms.
synonymA word or term having exactly or very nearly the same meaning as another word or term.
taxonomyA collection of controlled vocabulary terms organized into a hierarchical structure. Each term in a taxonomy is in one or more parent/child (broader/narrower) relationships to other terms in the taxonomy.
termOne or more words designating a concept. See also compound term, entry term, and precoordinated term.
thesaurusA controlled vocabulary arranged in a known order and structured so that the various relationships among terms are displayed clearly and identified by standardized relationship indicators. Relationship indicators should be employed reciprocally.
top termThe broadest term in a controlled vocabulary hierarchy, sometimes indicated by the abbreviation TT.
vocabulary controlThe process of organizing a list of terms (a) to indicate which of two or more synonymous terms is authorized for use; (b) to distinguish between homographs; and (c) to indicate hierarchical and associative relationships among terms in the context of a controlled vocabulary or subject heading list. See also controlled vocabulary.