A state is a set of institutions that possess the authority to make the rules that govern the people in one or more societies, having internal and external sovereignty over a definite territory. In Max Weber's influential definition, it is that organization that has a "monopoly on the legitimate use of physical force within a given territory." It thus includes such institutions as the armed forces, civil service or state bureaucracy, courts, and police.

Although the term often refers broadly to all institutions of government or rule—ancient and modern—the modern state system bears a number of characteristics that were first consolidated in western Europe, beginning in earnest in the 15th century, when the term "state" also acquired its current meaning. Thus the word is often used in a strict sense to refer only to modern political systems.

Within a federal system, the term state also refers to political units, not sovereign themselves, but subject to the authority of the larger state, or federal union, such as the "states and territories of Australia" and the "states" in the United States.

In casual usage, the terms "country," "nation," and "state" are often used as if they were synonymous; but in a more strict usage they can be distinguished:

• Country denotes a geographical area
• Nation denotes a people who share common customs, origins, and history. However, the adjectives national and international also refer to matters pertaining to what are strictly states, as in national capital, international law
• State refers to set of governing institutions that has sovereignty over a definite territory