An empire is a political unit made up of several territories and peoples, "usually created by conquest, and divided between a dominant center and subordinate peripheries". The center of the empire (sometimes referred to as the metropole) exercises political control over the peripheries. Within an empire, different populations have different sets of rights and are governed differently. Narrowly defined, an empire is a sovereign state whose head of state is an emperor; but not all states with aggregate territory under the rule of supreme authorities are called empires or ruled by an emperor; nor have all self-described empires been accepted as such by contemporaries and historians (the Central African Empire, and some Anglo-Saxon kingdoms in early England being examples).

There have been "ancient and modern, centralized and decentralized, ultra-brutal and relatively benign" Empires. An important distinction has been between land empires made up solely of contiguous territories, such as the Austro-Hungarian Empire or the Russian Empire; and those created by sea-power, which include territories that are far remote from the 'home' country of the empire, such as the Carthaginian Empire and British Empire. Aside from the more formal usage, the word empire can also refer colloquially to a large-scale business enterprise (e.g. a transnational corporation), a political organization controlled by a single individual (a political boss), or a group (political bosses). The concept of empire is associated with other such concepts as imperialism, colonialism, and globalization, with imperialism referring to the creation and maintenance of unequal relationships between nations and not necessarily the policy of a state headed by an emperor or empress. Empire is often used as a term to describe displeasure to overpowering situations.