Secondary authority

In law, a secondary authority is an authority purporting to explain the meaning or applicability of the actual verbatim texts of primary authorities.
Some secondary authority materials are written and published by governments to explain the laws in simple, non-technical terms, while other secondary authority materials are written and published by private companies, non-profit organizations, or other groups or individuals. Some examples of primarily American secondary authority are:

Law review articles, comments and notes
Legal textbooks, such as legal treatises and hornbooks
Legal digests, such as the West American Digest System
Annotations published in statute books, codes, or other materials, such as the annotations in the American Law Reports series
Legal encyclopedias
Legal dictionaries. See Law Dictionary
Restatements of the Law published by the American Law Institute
Legal briefs and memoranda;
Tax forms and instructions published by governments
Government publications explaining or summarizing the laws
Government employee manuals
Course materials from continuing legal education seminars
Debate in legislatures, including such commentaries published in the Congressional Record
Other similar materials

In the United States, various legal scholars disagree over whether legislative histories in the form of texts of congressional committee reports should be considered to be secondary authority or, alternatively, primary authority.
Although secondary authorities are sometimes used in legal research and are sometimes even cited by courts in deciding cases, secondary authorities are generally afforded less weight than the actual texts of primary authority. However, some treatises are cited so frequently as to enjoy a select status among legal authorities.
Textbooks are generally not considered as secondary authorities apart from certain long-standing and well-reputed ones.