Description
Citations are explicit references in scientific/scholarly literature (books, edited volumes, journals, scientific forums) to research products or outputs.
Explanation
Citations, in the sense of references, can be interpreted as evidence of use and thus of impact on peers. They occur in footnotes or endnotes in books, edited volumes and journals, and in scientific/scholarly forums provide material support for a scientific or scholarly claim.
References as used in certain prescribed domains or subdomains of the humanities can be analysed using standardised methods, in the form of citation analyses. That is not true in other domains, however, and references there will have to be presented as part of the narrative.
Usefulness
References can be presented in the narrative as evidence of use by peers.
See also Robust Data