keyword — One of a set of keywords describing the content of a document
Keyword is a term describing the content of a document. The keyword applies to the document component that contains it.
Keywords are rarely displayed to a reader. Usually, they are reserved for searching and retrieval purposes. If they are displayed, they may be displayed either inline or as a displayed block, depending on context.
SubjectTerms, which should be drawn from a controlled vocabulary, keywords may be chosen freely.