Primary Sources: A primary source is a source of information that was created during the time under study. Primary sources can be anything from documents to artifacts to photographs to recordings to social media posts.
Secondary Sources: A secondary source is an analytical work created by researching primary sources and other secondary sources. Secondary sources include books, articles, reviews, textbooks, biographies, and indexes.
Tertiary Sources: A tertiary source is a synthesis of topics generated from related primary and secondary sources. Examples include timelines, chronologies, bibliographies, directories, handbooks, and encyclopedia entries.
Definitions modified from Stony Brook University Libraries.