Citation, n. "A reference to a legal precedent or authority, such as a case, statute, or treatise, that either substantiates or contradicts a given position. -- Often shortened to cite." Citation, Black's Law Dictionary (10th ed. 2014).
There are several different systems for legal citation which are listed below in the box titled Legal Citation Manuals/Guides. Whichever system you're using, there are a few main tenets of citation to keep in mind:
User's Guide to the "Bluebook" by Many other libraries have research guides to help their students learn and understand legal citation principles. A few are listed here, and the last entry provides steps to finding additional guides.