A polity is any kind of political entity. It is a group of people who are collectively united by a self-reflected cohesive force such as identity, who have a capacity to mobilise resources, and are organised by some form of institutionalised hierarchy.
A polity can be manifested in many different forms, such as a state, an empire, an international organization, a political organisation and other identifiable, resource-manipulating organisational structures. A polity, like a state, does not need to be a sovereign unit. The most preeminent polities today are Westphalian states and nation-states, commonly (though incorrectly) referred to as "nations".
It therefore encapsulates a vast multitude of organisations, many of which form the fundamental apparatuses of contemporary states such as their subordinate civil and local government authorities. Polities do not need to be in control of any geographic areas, as not all political entities and governments have controlled the resources of one fixed geographic area. The historical Steppe Empires originating from the Eurasian Steppe are the most prominent example of non-sedentary polities. These polities differ from states because of their lack of a fixed, defined territory. Empires also differ from states in that their territories are not statically defined or permanently fixed, and consequently that their body politic was also dynamic and fluid.
It is useful, then, to think of a polity as a political community. A polity can be defined either as a faction within a larger (usually state) entity or, at different times, as the entity itself. Kurds in Iraqi Kurdistan, for example, are parts of their own separate and distinct polity. They are also, though, members of the sovereign state of Iraq which is itself a polity, albeit one which is much less specific and, as a result, much less cohesive. It is therefore possible for an individual to belong to more than one polity at a time.