Definition: Tertiary sources of information include expenditure that
summarizes and systematizes knowledge expressed in primary and secondary
sources. Usually, tertiary sources present information in a systematic and
compact way, providing references to the original sources. Those includes, for
example, dictionaries, encyclopedias, manuals, textbooks, bibliographies,
databases.
Tertiary resources often provide data in more convenient form and can provide context helpful in interpreting information in primary and secondary sources.