The collection of binding customs or rules of a community prescribed, formally recognized or enforced by a community or controlling authority. When you use this tag, please consider if your question might be more appropriate on law.stackexchange.com.
Questions with the Law tag reference laws either singly or as a body. The tag itself is taken as a noun referring to:
The principles and regulations established in a community by some authority and applicable to its people, whether in the form of legislation or of custom and policies recognized and enforced by judicial decision.
Any written or positive rule or collection of rules prescribed under the authority of the state or nation, as by the people in its constitution. Compare bylaw, statute law. Source: Dictionary.com
In the United States, law is at the intersection of the judiciary, who interpret and apply the rules; the government, that is responsible for making rules; and the people with whom rests the ultimate authority for the body of laws, as exercised through the political system.
There are different systems of laws - Civil Law, Religious Law and Common Law. In the U.S. Common Law, based on both statue and precedent is used. Religious law is entirely separate from the government - the province only of churches and religious bodies. The First amendment of the U.S. constitution, through the establishment clause and the free exercise clause ("Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof ...") is a foundation for this separation.
The U.S. Constitution is the foundation and supreme law for all U.S. laws, rules, statutes created by governments (federal, state and local). Laws made as well as judicial precedents are ultimately measured against the constitution.