Law is a system of rules created and enforced by social or governmental institutions to regulate behavior. Its precise definition has been the subject of long debate, but four main purposes are commonly cited: establishing standards, maintaining order, resolving disputes, and protecting liberties and rights. Law is a broad term that can be applied to a wide variety of fields, such as criminal and civil laws, contracts, property, and the law of war.

The law is a human creation, and as such it is highly contingent on the actions of humans and their minds. It is impossible to empirically prove the contents of any particular law, but it is equally difficult to determine whether or not a particular set of laws should comprise precepts of such and such import:

As a result, it is important to distinguish between law as it exists in reality and as it has been perceived and articulated by different groups of people. A key issue is the extent to which a government, or a group of people acting together, can legitimately extend their power over the lives of individuals within their territory. This question has been the source of many books and arguments, and modern military, policing and bureaucratic power over ordinary citizens poses special challenges that earlier writers such as Locke and Montesquieu did not anticipate.

There are also a number of distinct legal fields, each with its own terminology and practices:

Generally speaking, law encompasses the legal systems of nations and states, as well as international agreements, treaties, and conventions. The law also refers to the profession of lawyers, judges, and other legal officials.

A specific field of law can be considered an aggregation of the rules of a given area, such as commerce, aviation, or medical jurisprudence. In addition, law can include a body of legal rules created by the courts themselves:

The judicial branch of a state or country’s government is referred to as the “law-making” branch, and is responsible for enforcing the law and deciding cases. Judges presiding over cases are known as justices, and they can be grouped into panels of three or more, called a bench, or en banc when all members of a court participate, rather than the usual quorum. Appellate courts, such as the Supreme Court of the United States, can also hold sessions en banc. These sessions are generally reserved for especially significant or precedent-setting cases. They can have the effect of reshaping legal doctrine and practice, or setting national policy. A judge may also create binding precedents, or rulings on a particular issue that are required to be followed by lower courts with authority to review those decisions. This is a common way to ensure consistency and fairness in the application of the law. These rulings are known as case law.