Common law, also known as case law or precedent, is law developed by judges through decisions of courts and similar tribunals rather than through legislative statutes or executive branch action. A "common law system" is a legal system that gives great precedential weight to common law, on the principle that it is unfair to treat similar facts differently on different occasions. The body of precedent is called "common law" and it binds future decisions. In cases where the parties disagree on what the law is, an idealized common law court looks to past precedential decisions of relevant courts. If a similar dispute has been resolved in the past, the court is bound to follow the reasoning used in the prior decision (this principle is known as stare decisis). If, however, the court finds that the current dispute is fundamentally distinct from all previous cases (called a "matter of first impression"), judges have the authority and duty to make law by creating precedent. Thereafter, the new decision becomes precedent, and will bind future courts. In practice, common law systems are considerably more complicated than the idealized system described above. The decisions of a court are binding only in a particular jurisdiction, and even within a given jurisdiction, some courts have more power than others. For example, in most jurisdictions, decisions by appellate courts are binding on lower courts in the same jurisdiction and on future decisions of the same appellate court, but decisions of lower courts are only non-binding persuasive authority. Interactions between common law, constitutional law, statutory law and regulatory law also give rise to considerable complexity. However stare decisis, the principle that similar cases should be decided according to consistent principled rules so that they will reach similar results, lies at the heart of all common law systems. Common law legal systems are in widespread use, particularly in England where it originated in the Middle Ages, and in nations that trace their legal heritage to England as former colonies of the British Empire, including the United States, Malaysia, Singapore, Pakistan, Sri Lanka, India, Ghana, Cameroon, Canada, Ireland, New Zealand, South Africa, Hong Kong and Australia.
The term common law has three main connotations and several historical meanings worth mentioning:
1. Common law as opposed to statutory law and regulatory law This connotation distinguishes the authority that promulgated a law. For example, most areas of law in most Anglo-American jurisdictions include "statutory law" enacted by a legislature, "regulatory law" promulgated by executive branch agencies pursuant to delegation of rule-making authority from the legislature, and common law or "case law", i.e., decisions issued by courts (or quasi-judicial tribunals within agencies).  This first connotation can be further differentiated into (a) pure common law arising from the traditional and inherent authority of courts to define what the law is, even in absence of an underlying statute, e.g., most criminal law and procedural law before the 20th century, and even today, most of contract law and the law of torts, and (b) court decisions that decide the fine boundaries and distinctions in law promulgated by other bodies, such as judicial interpretations of the Constitution, of statutes, and of regulations.
2. Common law legal systems as opposed to civil law legal systems This connotation differentiates "common law" jurisdictions and legal systems from "civil law" or "code" jurisdictions. Common law systems place great weight on court decisions, which are considered "law" with the same force of law as statutes. By contrast, in civil law jurisdictions (the legal tradition that prevails in, or is combined with common law in, Europe and most non-Islamic, non-common law countries), judicial precedent is given less weight...