A bibliographic reference is a description of some publication that uniquely identifies it, providing the information needed to retrieve the associated document. A reference is distinguished from a citation, which occurs in the body of a document and points to a reference. Note that references are distinguished from documents as well.
The information associated with a reference is contained in data fields, which are binary relations (often unary functions).
A reference should at least contain information about the author, title, and year. (Since there are exceptions, that constraint is associated with a specialization of this class.) .