National interest refers to the goals, values, and objectives that a state seeks to promote and protect in its foreign policy. The concept of national interest encompasses a wide range of considerations, including economic prosperity, security, and the promotion of national values and ideology. National interest is often used to guide the development of foreign policy and to evaluate the costs and benefits of different international actions. The definition and interpretation of national interest can vary widely depending on political and ideological factors, as well as on the specific circumstances and challenges facing a state.
Source: Morgenthau, H. J. (1948). Politics among nations: the struggle for power and peace. New York: Alfred A. Knopf.