Law is a set of rules enforced by social or governmental institutions that regulate human behaviour and protect property, individuals, and groups. The precise definition is debated, but it generally covers such topics as contract; torts; criminal law; and administrative law (regulation of public utilities like water, electricity, gas and telecommunications).
Law encompasses many sub-fields. Some are: air law; bankruptcy; civil procedure; evidence law; maritime law; medical jurisprudence; and tax law.
The chief functions of law are establishing standards, maintaining order and resolving disputes. These are achieved through a combination of legislative, executive and judicial processes. The exact nature of these processes differ from nation to nation. Some have an almost military structure, with armed forces controlling political-legal authority. Others are democratic, and have the aspiration of giving citizens more rights than they currently enjoy under existing power structures.
The content of laws is largely dependent on the shape and limitations of the physical world. It is thus impossible to empirically verify whether they contain precepts of such-and-such import. This makes the content of law normative, as opposed to descriptive or causal (as in the laws of gravity and supply and demand in economics).
There is a great deal of case law, and the decisions made by courts are binding precedent unless challenged on the grounds of bad law or significantly different facts. Briefs are written documents submitted by lawyers for each side in a case that explain to the judge why the judge should decide the case in favour of their client.