Polarity in international relations is a description of the distribution of power within the international system. It describes the nature of the international system at any given period of time. There are three types of systems, Unipolarity, Bipolarity, and Multipolarity. The type of system is completely dependent on the distribution of power and influence of states in a region or internationally.
Unipolarity in international politics describes a distribution of power in which there is one state with most of the cultural, economic, and military influence. This is also called a hegemony or hyperpower.
Bipolarity in international politics describes a distribution of power in which two states have the majority of economic, military, and cultural influence internationally or regionally. Often, spheres of influence would develop. For example, in the Cold War, most Western and democratic states would fall under the influence of the USA, while most Communist states would fall under the influence of the USSR. After this, the two powers will normally maneuver for the support of the unclaimed areas.
The bipolar system can be said to extend to much larger systems, such as alliances or organizations, which would not be considered nation-states, but would still have power concentrated in two primary groups.
