Multilateralism is the practice of multiple nations working together on a particular issue or policy. It involves cooperation among multiple states to achieve common goals and address global challenges. Multilateralism is often contrasted with bilateralism, which involves cooperation between only two states. The use of multilateralism can help to increase the legitimacy and effectiveness of international actions and can be seen as a way to address global issues that cannot be solved by individual states acting alone.
Source: Ruggie, J. G. (1982). International regimes, transactions, and change: embedded liberalism in the postwar economic order. International Organization, 36(2), 379-415