Courtesy: Univ. of Waterloo
Primary sources are original materials/information on which other research is based. They include:
e.g. of Grey Lit: Preprint servers for Biology, Math, Comp Sci, Physics etc (Grey Lit)
Secondary sources analyses, evaluates, interprets or summarizes information reported by researchers in the primary literature. These include:
Tertiary sources consist of primary and secondary source information which has been collected and distilled. Some examples: