What is Contractarianism or Contractualism?

Contractarianism or Contractualism refers to a political theory of legitimacy and moral. This theory settles the beginnings of moral norms. Moral norms derive from the idea of mutual agreement.

“Contractualism is a term in philosophy that refers either to a family of political theories in the social contract tradition (when used in this sense, the term is synonymous with contractarianism)  or to the ethical theory developed in recent years by T. M. Scanlon, especially in his book What We Owe to Each Other.

Social contract theorists from the history of political thought include Hugo Grotius (1625), Thomas Hobbes (1651), Samuel Pufendorf (1673), John Locke (1689), Jean-Jacques Rousseau (1762), and Immanuel Kant (1797); more recently, John Rawls (1971), David Gauthier (1986) and Philip Pettit (1997).” https://en.wikipedia.org/wiki/Contractualism