What is harvard reference system？

准确地说应该是harvard referencing system

Harvard referencing is a citation system developed by Harvard University and used by publishers all over the world. It also known as the parenthetical system, and the author-date system. This citation system is increasingly preferred by scholars and professional writers as being less cumbersome than footnotes.
Under the Harvard referencing system, book titles are cited in the text in parentheses after the sentence, using the surname of the author and the year only, with the parentheses closing before the period, as in (Author 2005). Newspaper articles may be cited by newspaper title (The Guardian 2005) or by the byline, as in (Bowcott 2005).

If the same author has published two books in 2005, and both are being referenced in the text, this is written as (Author 2005a) and (Author 2005b). In the case of multiple newspaper-article citations in the same text, the date of the articles is used, as in (The Guardian, October 18