A secondary source is a source about an event, person, or place, usually based on the analysis or interpretation of primary source materials. Examples include academic articles and books. Keep in mindthat a secondary source could be a primary source depending on your research focus. For example, a book about U.S. history written in the 1950s is a secondary source, unless you are studying how history was studied in the 1950s, in which case the book becomes a primary source.
Secondary sources can be useful in tracking down primary sources, and they also can help provide a context for the primary sources you use. For these reasons, you may want to find some secondary sources as you conduct your research for your DBQ.