Broadly, a citation is a reference to a published or unpublished source.
Reference is a relation between objects in which one object designates, or acts as a means by which to connect to or link to, another object.
MLA Citations by professorrome
More precisely, a citation is an abbreviated alphanumeric expression embedded in the body of an intellectual work that denotes an entry in the bibliographic references section of the work for the purpose of acknowledging the relevance of the works of others to the topic of discussion at the spot where the citation appears.
APA Style: In-text Citations, Quotations, and Plagiarism by Samuel Forlenza
Generally the combination of both the in-body citation and the bibliographic entry constitutes what is commonly thought of as a citation.
References to single, machine-readable assertions in electronic scientific articles are known as nanopublications, a form of microattribution.
The term microattribution was first defined as "giving database accessions the same citation conventions and indices that journal articles currently enjoy".
Citations have several important purposes: to uphold intellectual honesty, to attribute prior or unoriginal work and ideas to the correct sources, to allow the reader to determine independently whether the referenced material supports the author's argument in the claimed way, and to help the reader gauge the strength and validity of the material the author has used.
Intellectual honesty is an applied method of problem solving, characterized by an unbiased, honest attitude, which can be demonstrated in a number of different ways:
As Roark and Emerson have argued, citations relate to the way authors perceive the substance of their work, their position in the academic system, and the moral equivalency of their place, substance, and words.
Despite these attributes, many drawbacks and shortcoming of citation practices have been reported, including for example honorary citations, circumstantial citations, discriminatory citations, selective and arbitrary citations.
The forms of citations generally subscribe to one of the generally accepted citations systems, such as the Oxford, Harvard, MLA, American Sociological Association, American Psychological Association, and other citations systems, because their syntactic conventions are widely known and easily interpreted by readers.
The American Psychological Association is the largest scientific and professional organization of psychologists in the United States, with around 117,500 members including scientists, educators, clinicians, consultants, and students.
The American Sociological Association, founded in 1905 as the American Sociological Society, is a non-profit organization dedicated to advancing the discipline and profession of sociology.
Each of these citation systems has its advantages and disadvantages.
Editors often specify the citation system to use.
Bibliographies, and other list-like compilations of references, are generally not considered citations because they do not fulfill the true spirit of the term: deliberate acknowledgement by other authors of the priority of one's ideas.