APA stands for the American Psychological Association and is the format designed for use within the field of psychology. However, other disciplines use APA as well, so always use the format your professor chooses.
The Publication Manual of the American Psychological Association, Seventh Edition is the official source for APA Style. With millions of copies sold worldwide in multiple languages, it is the style manual of choice for writers, researchers, editors, students, and educators in the social and behavioral sciences, natural sciences, nursing, communications, education, business, engineering, and other fields.