CitationA citation is a credit or reference to another document or source. There are many rules for the format and use of such citations in different fields:
Varying rules and practices for citations apply in a science, a law, a theological citing of authority (e.g. the isnah which "back" the hadith in Islam), the prior art that applies in patent law, or marks applied in copyright.
Definitions of plagiarism, uniqueness or innovation, trustworthiness or reliability vary so widely among these fields that the use of citations has no simple common practice. In any of these fields the concept of a citation index can apply, which summarizes published citations of a given publication.
A citation, in law, can also mean an official summons to appear before a court.