What is "citator"

Citator \Ci*ta"tor\, n. One who cites. [R]

n. (context legal English) An index of citations of legal cases and other sources

In legal research, a citator is a citation index of legal resources, one of the best-known of which in the United States is Shepard's Citations. Given a reference of a legal decision, a citator allows the researcher to find newer documents which cite the original document and thus to reconstruct the judicial history of cases and statutes. Using a citator in this way is colloquially referred to as "Shepardizing".