an international organization of nations pledged to promote world peace and security,maintain treaty obligations & the observance of international law, & cooperate in furthering social progress: the organization was formed in San Francisco in 1945 under a permanent charter (ratified by 50 countries) that had its inception in conferences (1941-45) held by nations opposed to the fascist coalition of Germany, Japan, Italy, & their satellites: the headquarters has been in New York City since 1946 and the membership (Feb., 2010) consists of 192 nations