What is the difference between primary and secondary sources?
A primary source is an original document or a record of a firsthand account of an historical event. Primary sources include original manuscripts, correspondence, diaries, memoires, photographs and film footage, statistics and legal records. Primary sources may also include drawings, posters, inscriptions on monuments or tombstones, and writings by observers.
Secondary sources are those that describe historical events. An article or book written by an author who was not present at the event would be a secondary source.
Your professor may have different defintions of primary and secondary sources depending on the subject you are studying. For more on primary and secondary sources, please see this site for examples and definitons: http://www.sccollege.edu/Library/Pages/primarysources.aspx.