Primary sources: A first description of original research conducted by authors, including methodology and results.
Below is an example of a primary source: a scholarly journal article from the journal Acta Biomaterialia that examines the effects of humidity on gecko setae.
Secondary sources: Literature that synthesizes information produced in primary literature. They are secondary because they are at least one step removed from the primary sources they discuss.
Below is an example of a secondary source: a scholarly review article from the journal Micromachines that summarizes self-cleaning surfaces, some of which are inspired by gecko setae.
Tertiary sources: Information further distilled from primary and secondary formats. When conducting research, it can be very helpful to consult tertiary sources to orient yourself to a topic. Tertiary sources can provide basic background information and can clue you in to helpful keywords.
Below is an example of a section on gecko setae from a tertiary source: Encyclopedia of Adaptations in the Natural World.