The description of what constitutes a primary source will vary from one discipline to another. This guide is intended to assist mainly those working in the humanities and social sciences (and particularly history).
In the natural sciences, a primary source generally refers to original research or ideas. Research articles, particularly those sections dealing with methods and results, often contain primary source material. For additional information regarding the different types of scientific literature, click here.
Within the humanities and social sciences, “Primary sources provide first-hand testimony or direct evidence concerning a topic under investigation. They are created by witnesses or recorders who experienced the events or conditions being documented. Often these sources are created at the time when the events or conditions are occurring, but primary sources can also include autobiographies, memoirs, and oral histories recorded later. Primary sources are characterized by their content, regardless of whether they are available in original format, in microfilm/microfiche, in digital format, or in published format.” (Yale University)
This video from the University of California-San Diego may be helpful in understanding primary sources.