Primary sources are firsthand accounts of events, recorded or produced by witnesses or recorders who were present at the time of the event or experienced the conditions being documented. Primary sources are characterized by their content, not their format. A primary source can be in a database, on microfilm, in print, etc.
Secondary sources are works that interpret or analyze an event or phenomenon. It is generally at least one-step removed from the event. Examples include scholarly or popular books and articles, reference books, and textbooks.