APA style (also known as APA format) is a writing style and format for academic documents such as scholarly journal articles and books. It is commonly used for citing sources within the field of behavioral and social sciences. It is described in the style guide of the American Psychological Association (APA), which is titled the Publication Manual of the American Psychological Association.(source: Wikipedia)
MLA Handbook (9th ed., 2021), formerly MLA Handbook for Writers of Research Papers (1977–2009), establishes a system for documenting sources in scholarly writing. It is published by the Modern Language Association, which is based in the United States. According to the organization, their MLA style "has been widely adopted for classroom instruction and used worldwide by scholars, journal publishers, and academic and commercial presses"(source: Wikipedia)
Parenthetical referencing, also known as Harvard referencing, is a citation style in which partial citations—for example, "(Smith 2010, p. 1)"—are enclosed within parentheses and embedded in the text, either within or after a sentence. They are accompanied by a full, alphabetized list of citations in an end section, usually titled "references", "reference list", "works cited", or "end-text citations"(source: Wikipedia)
The Chicago Manual of Style (abbreviated in writing as CMOS or CMS, or sometimes as Chicago) is a style guide for American English published since 1906 by the University of Chicago Press. Its 17 editions have prescribed writing and citation styles widely used in publishing.The guide specifically focuses on American English and deals with aspects of editorial practice, including grammar and usage, as well as document preparation and formatting.(source: Wikipedia)