In the sciences, a primary source describes original research, while a secondary source analyzes or comments on a primary source or sources. For example, a research article is primary literature because it describes an original experiment and its results, while a review article is secondary literature because it collates multiple research articles to describe the current state of the field. A tertiary source is an index or consolidation of primary and secondary sources.
Offered by a consortium of 12 major US and UK botanical and natural history libraries with a collection of 46,000-plus titles and 90,000-plus volumes. The biodiversity-related items range in date from 1450 to the present.