A polity is any kind of political entity. It is a group of people that are collectively united by a self-reflected cohesive force such as identity, that have a capacity to mobilise resources, and are organised by a few form of institutionalised hierarchy.
A polity can be manifested in a large number of different forms such as a state, an empire, an international organization, a political organisation and additional identifiable, resource-manipulating organisational structures. A polity, like a state, doesn't need to be a sovereign unit. The most preeminent polities today are Westphalian states and nation-states, commonly (however, incorrectly) referred to as "nations".
It therefore encapsulates a vast multitude of organisations, a large number of of which form the fundamental apparatuses of contemporary states such as their subordinate civil and local government authorities. Polities don't 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 additionally differ from states in that their territories aren't statically defined or permanently fixed, and consequently that their body politic was additionally 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.
Thomas Hobbes was a highly significant figure in the conceptualisation of polities, and in particular of states. Hobbes considered notions of the state and the body politic in his most notable work, Leviathan.
In previous centuries, body politic was additionally understood to mean "the physical person of the sovereign:" emperor, king or dictator in monarchies and despotisms, and the electorate in republics. As a large number of polities have become more democratic in the last few centuries the body politic, where sovereignty is bestowed, has grown to a much greater size than simply the ruling elite, such as the monarchy. In present times, it might additionally refer to representation of a group, such as ones drawn along ethnic or gender lines. Cabinets in liberal democracies are chosen to represent the body politic.