West Berlin refers to the western part of Berlin during the period when Germany was divided into East and West. It was controlled by the democratic western powers (US, UK, France), while East Berlin was under Soviet control.
Related terms
Iron Curtain: The metaphorical division between communist Eastern Europe (controlled by the USSR) and democratic Western Europe.
Berlin Wall: A physical barrier constructed by the German Democratic Republic (East Germany) that divided West Berlin from East Berlin and prevented movement between the two parts of the city.
Truman Doctrine: A policy implemented by President Truman stating that the United States would provide political, military, and economic assistance to all democratic nations facing internal or external threats.