A primary source was created or recorded during the time it occurred, or created/recorded by someone who was present during the experience or time period. Examples can include:
Constitution of the United States by Photography with Jack is licensed under CC BY-NC-SA 2.0.
Secondary sources are one or more sources removed from the actual event; they offer an analysis of primary sources, or attempt to explain or describe those primary sources. Examples can include:
Unlike the Constitution pictured on the left, a book ABOUT the constitution is a secondary source.
Primary source: An interview of a witness of 9/11
Secondary source: Book written about 9/11 by someone who wasn't there
Primary source: Article in a scholarly journal reporting the research and methodology of an experiment or study
Secondary source: Articles analyzing and commenting on the results of original research, sometimes called review articles
Primary source: Declaration of Independence
Secondary source: A book or article analyzing the Declaration of independence
Primary source: Song lyrics
Secondary source: An essay analyzing the lyrics of a song
Primary source: Congressional hearing on steroid abuse in Major League Baseball
Secondary source: A newspaper or magazine article reporting on the hearings
Primary source: Diary of a soldier in the Confederate Army
Secondary source: Book about the United States Civil War
Primary source: H1N1 flu statistics gathered by the Center for Disease Control (a government agency)
Secondary source: A newspaper or magazine article about the H1N1 flu.