Case of first impression

In legal systems based on common law, a precedent, or authority, is a principle or rule established in a previous legal case that is either binding on or persuasive for a court or other tribunal when deciding subsequent cases with similar issues or facts. Common law legal systems place great value on deciding cases according to consistent principled rules so that similar facts will yield similar and predictable outcomes, and observance of precedent is the mechanism by which that goal is attained. The principle by which judges are bound to precedents is known as stare decisis. Black's Law Dictionary defines "precedent" as a "rule of law established for the first time by a court for a particular type of case and thereafter referred to in deciding similar cases."Common law precedent is a third kind of law, on equal footing with statutory law (statutes and codes enacted by legislative bodies), and Delegated legislation (in U.K. parlance) or regulatory law (in U.S. parlance) (regulations promulgated by executive branch agencies).

Case law, in common law jurisdictions, is the set of decisions of adjudicatory tribunals or other rulings that can be cited as precedent. In most countries, including most European countries, the term is applied to any set of rulings on law which is guided by previous rulings, for example, previous decisions of a government agency.

Essential to the development of case law is the publication and indexing of decisions for use by lawyers, courts and the general public, in the form of law reports. While all decisions are precedent (though at varying levels of authority as discussed throughout this article), some become "leading cases" or "landmark decisions" that are cited especially often.

Stare decisis (Anglo-Latin pronunciation: /ˈsteɪriː dᵻˈsaɪsᵻs/) is a legal principle by which judges are obligated to respect the precedent established by prior decisions. The words originate from the phrasing of the principle in the Latin maxim Stare decisis et non quieta movere: "to stand by decisions and not disturb the undisturbed." In a legal context, this is understood to mean that courts should generally abide by precedent and not disturb settled matters. The principle of stare decisis can be divided into two components.

...
Wikipedia