From The Art and Popular Culture Encyclopedia
In common law legal systems, a precedent or authority is a legal case establishing a principle or rule that a court or other judicial body adopts when deciding subsequent cases with similar issues or facts.
The precedent on an issue is the collective body of judicially announced principles that a court should consider when interpreting the law. When a precedent establishes an important legal principle, or represents a new or changed law on a particular issue, that precedent is often known as a landmark decision.
Precedent is central to legal analysis and rulings in countries that follow common law like the United Kingdom (except Scotland which retains its own legal system) and Canada (except Quebec). In some systems precedent is not binding but is taken into account by the courts.