social contract

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A usually implicit agreement among the members of an organized society or between the governed and the government defining and limiting the rights and duties of each.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun philosophy, politics An implicit agreement or contract among members of a society that dictates things such as submission of individuals to rule of law and acceptable conduct.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an implicit agreement among people that results in the organization of society; individual surrenders liberty in return for protection