Primary Source: An authoritative document relating to a subject, which is used in the preparation of a later work, such as an original record or a contemporary document. In the humanities, a primary source is the document being analyzed; in the sciences it is a journal article reporting the results of original research. Primary sources are also called original sources or source material.
Secondary Source: A publication that digests, analyzes, evaluates, and/or interprets the information in primary sources.
Tertiary Source: A source that compiles, analyzes, and/or digests secondary sources.
More information: Primary vs. Secondary vs. Tertiary
Examples of types of sources.