These are original materials which have not been filtered through interpretation, condensation, or often, even evaluation by a second party. Some primary sources are not published such as oral accounts by one person to another. Where primary sources are available in a library they may be listed in secondary sources such as indexes, abstracts, and bibliographies. Archives often box like materials, such as one person's correspondence, and in these cases materials may not be indexed at all. A secondary source interprets and analyses primary sources.
Secondary sources are one step removed from the event.
Examples of secondary sources are biographies as opposed to original memoirs or auto-biography and sources which index and organize the primary literature. The distinction between primary and secondary sources is not always apparent. For example, a person at a meeting may not be stating original views but simply repeating what he or she has read or heard from someone else. A journal article is a primary source if it represents original thinking or a report on a discovery but the same journal may include secondary materials which are reports or summaries of the findings of others. These consist of information which is a distillation and collection of primary and secondary sources.