A primary source is an original record or artifact created at the time an historical event occurred. A primary source comes from an eyewitness to the event or historical period. This includes letters, speeches, newspapers, interviews, memoirs, government documents, photographs, maps, audio recordings, moving pictures, research data, and objects like works of art, buildings, tools, and weapons.
With a primary source, there are no degrees of separation. The closer to the actual event a book or object is, then the more likely it will be a primary source.
As the American Library Association says, "These sources serve as the raw material to interpret the past. . ."