In common law legal systems, a precedent or authority is a principle or rule established in a legal case that a court or other judicial body may apply when deciding subsequent cases with similar issues or facts. 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.”[1]
In other words precedent can be defined as “an already decided decision which furnishes the basis for later cases involving

similar facts and issues.”

TYPES OF PRECEDENT — Binding precedent

Precedent that must be applied or followed is known as binding precedent (alternately metaphorically precedent, mandatory or binding authority, etc.). Under the doctrine of stare decisis, a lower court must honor findings of law made by a higher court that is within the appeals path of cases the court hears. In state and federal courts in the United States of America, jurisdiction is often divided geographically among local trial courts, several of which fall under the territory of a regional appeals court. All appellate courts fall under a highest court (sometimes but not always called a “supreme court”). By definition, decisions of lower courts are not binding on courts higher in the system, nor are appeals court decisions binding on local courts that fall under a different appeals court. Further, courts must follow their own proclamations of law made earlier on other cases, and honor rulings made by other courts in disputes among the parties before them pertaining to the same pattern of facts or events, unless they have a strong reason to change these rulings (see Law of the case re: a court’s previous holding being binding precedent for that court).
One law professor has described mandatory precedent as follows:
Given a determination as to the governing jurisdiction, a court is “bound” to follow a precedent of that jurisdiction only if it is directly in point. In the strongest sense, “directly in point” means that: (1) the question resolved in the precedent case is the same as the question to be resolved in the pending case, (2) resolution of that question was necessary to the disposition of the precedent case; (3) the significant facts of the precedent case are also presented in the pending case, and (4) no additional facts appear in the pending case that might be treated as significant.[2]
In extraordinary circumstances a higher court may overturn or overrule mandatory precedent, but will often attempt to distinguish the precedent before overturning it, thereby limiting the scope of the precedent.
Under the U.S. legal system, courts are set up in a hierarchy. At the top of the federal or national system is the United States Supreme Court, and underneath are lower federal courts. The state court systems have hierarchy structures similar to that of the federal system.
The U.S. Supreme Court has final authority on questions about the meaning of federal law, including the U.S. Constitution. For example, when the Supreme Court says that the First Amendment applies in a specific way to suits for slander, then every court is bound by that precedent in its interpretation of the First Amendment as it applies to suits for slander. If a lower court judge disagrees with a higher court precedent on what the First Amendment should mean, the lower court judge must rule according to the binding precedent. Until the higher court changes the ruling (or the law itself is changed), the binding precedent is authoritative on the meaning of the law.
Although state courts are not part of the federal system, they are also bound by U.S. Supreme Court rulings on federal law. State courts are not generally bound by Federal District courts or Circuit courts, however.[3][4] A federal court interpreting state law is bound by prior decisions of the state supreme court.[5]
Lower courts are bound by the precedent set by higher courts within their region. Thus, a federal district court that falls within the geographic boundaries of the Third Circuit Court of Appeals is bound by rulings of the Third Circuit Court, but not by rulings in the Ninth Circuit, since the Circuit Courts of Appeals have jurisdiction defined by geography. The Circuit Courts of Appeals can interpret the law how they want, so long as there is no binding Supreme Court precedent. One of the common reasons the Supreme Court grants certiorari (that is, they agree to hear a case) is if there is a conflict among the circuit courts as to the meaning of a federal law.

TYPES OF PRECEDENT — Persuasive precedent

Precedent that is not mandatory but which is useful or relevant is known as persuasive precedent (or persuasive authority or advisory precedent). Persuasive precedent includes cases decided by lower courts, by peer or higher courts from other geographic jurisdictions, cases made in other parallel systems (for example, military courts, administrative courts, indigenous/tribal courts, state courts versus federal courts in the United States), and in some exceptional circumstances, cases of other nations, treaties, world judicial bodies, etc.
In a case of first impression, courts often rely on persuasive precedent from courts in other jurisdictions that have previously dealt with similar issues. Persuasive precedent may become binding through its adoption by a higher court.