After the main text of your article there is a section, usually headed References, containing bibliographic details of those publications that you have used for support in the main text. Each entry contains information about items such as author(s), date of publication, title, name of publication, and pages, given in at least sufficient detail to allow a reader to locate the work. In the main text you point to a particular reference with a cue or key. The cue+reference is a citation, but the cue or key is itself commonly called a citation, and I follow that custom here. There are many styles of citation (cue) and reference, and each journal makes its own choice. In many journals the ‘Instructions to Authors’ are vague about the citation and reference system to be used, and about formatting details for both, but you can infer these from examples in recent issues of the journal or get a reference program to use the journal format template if it offers one.

Author−date system

Here is an example of ‘author−date’ citations, sometimes called the Harvard system, in one style using space and ‘,’ as separators; ‘and’ to link two authors; ‘et al.’ for three or more authors; and multiple citations ordered by date: