"An original source, such as a speech, a diary, a novel, a legislative bill, a laboratory study, a field research report, or an eyewitness account. While not necessarily more reliable than a secondary source, a primary source has the advantage of being closely related to the information it conveys and as such is often considered essential for research, particularly in history. In the sciences, reports of new research written by the scientists who conducted it are considered primary sources."
*Hacker, D., & Fister, B. (2006). Research and documentation in the electronic age. Boston, MA: Bedford/St. Martin's.
Some examples of search terms to find primary sources:
You may get limited results searching for the word "autobiography" since the Library of Congress does not use that subject heading. Try searching for "biography" but then look to make sure that the author is also listed as a subject. That is your clue that the person is writing about him or herself, and that is a primary source.