index

Something that serves to guide, point out, or otherwise facilitate reference, especially.

An alphabetized list of names, places, and subjects treated in a printed work, giving the page or pages on which each item is mentioned.

A thumb index.

A table, file, or catalog.

A list of keywords associated with a record or document, used especially as an aid in searching for information.

Something that reveals or indicates; a sign.

A character (☞) used in printing to call attention to a particular paragraph or section.

An indicator or pointer, as on a scientific instrument.

A number or symbol, often written as a subscript or superscript to a mathematical expression, that indicates an operation to be performed, an ordering relation, or a use of the associated expression.