Authorities are the collection of sources of the law that an attorney refers to during a case. Examples include statutes, law text books, judicial decisions, and case laws. These authorities are used to help support the attorney's position. They can refer to them to help make an argument or support their position.
Attorneys use authorities to give legitimacy to their pleadings and arguments. In order to show that their argument is supported by the law, the attorney must be able to demonstrate this by referencing sources of the law. These are known as authorities. The authorities are the sources of the law that are used as references. An example of how an authority would be used in court is if an attorney cited a particular statute which gave credibility to their argument.