What are reference sources?
Reference sources are works that help you locate information about people, facts, and ideas. These sources can help you find the date of an important event, major achievements of an individual or organization, or a definition of a term or concept. They are sometimes called tertiary sources.
Examples include:
Dictionaries/encyclopedias (may also be secondary), almanacs, fact books, Wikipedia, bibliographies (may also be secondary), directories, guidebooks, manuals, handbooks, and textbooks (may be secondary), indexing and abstracting sources.