(semantics) The condition of a sign which has an empty, absent, non-existent, paradoxical, hypothetical, supernatural, or undefined referent, such as nothing, null, vacuum, or void.

(data management) Data describing a physical or virtual object and its properties.

The list of sources used or considered in preparing a work.

plural of reference book

A book providing factual information. / (libraries) A book that can be consulted in the library but cannot be borrowed.

plural of reference angle

An acute angle with the same values of trigonometric functions, up to sign, as another angle: used for easy reference when examining the non-acute angle.

(information science) A reference that specifies within some taxonomy or text typology one or more defined categories into which the referenced article, computer file etc. belongs.

plural of category reference

The false belief that random occurrences have a special connection to oneself.