Subject indexing is a vital process that identifies and assigns relevant subject tags or terms to various documents, books, and other forms of content. Synonyms for subject indexing include subject analysis, subject cataloging, subject heading, and subject classification. Subject analysis identifies the content of a document and assigns relevant subject terms to them. Subject headings serve as access points to a document's content, and subject classification groups similar materials under identical subject categories for easy access. In many cases, subject indexing is automated using computer algorithms, but some documents, such as those that require multiple interpretations, may need a human indexer to study and tag the subjects manually.