A primary source is a document or artifact that was created at the time of study and serves as an original source of information about a topic. Examples include correspondence, diaries, newspapers and interviews. Primary sources can also be produced at a later date in the form of memoirs or oral histories.
A secondary source is a document or artifact that discusses and relates to information presented in a primary source. They are usually created at a distance from the event or person being described and are used to interpret primary sources. Examples can include history books, biographies and scholarly journals. Think of these types of sources as “second-hand” sources of information. It is not a book written by The Citadel's female alumni; it is a book written about them.
A tertiary source is a source that indexes, abstracts and/or compiles other sources. Examples include dictionaries, encyclopedias, fact books and almanacs. Tertiary sources give an overview of a subject that can then lead to primary and secondary sources.