According to the Harvard University Library:
The Harvard Citation Style, also called the Harvard Referencing System or "Author-date Referencing"
The "Harvard System" is something of a misnomer, as there is no official institutional connection. It's another name for the author/date citation system, the custom of using author and date in parentheses, e.g. (Robbins 1987) to refer readers to the full bibliographic citations in appended bibliographies. Some Harvard faculty were among the first practitioners in the late 19th century, and the name stuck, particularly in England and the Commonwealth countries.
For detailed guidance on Author-Date Referencing see the following:
For more history on the "Harvard referencing style" see the following: