A secondary source uses information from a primary source, firsthand source, or other secondary source to describe or analyze a source. Secondary sources provide a subjective view of an account.
In the humanities, secondary sources examine interpretations of primary sources. In the sciences, secondary sources are those that examine original research findings. Examples of secondary sources include theses, research papers, abstracts, academic journal articles, popular media, textbooks and biographies. There is some discrepancy between what separates a secondary source and a tertiary source, which is a summary of multiple sources. Encyclopedias and textbooks are both secondary and tertiary sources, depending upon the approach.