Borders are geographical boundaries, imposed either by geographic features such as oceans, or by arbitrary groupings of political entities such as governments, sovereign states, federated states, and other subnational entities. Borders are established through warfare, colonization, or mutual agreements between the political entities that reside in those areas; the creation of these agreements is called boundary delimitation.
Some borders—such as most states' internal administrative borders, or inter-state borders within the Schengen Area—are open and completely unguarded. Most external borders are partially or fully controlled, and may be crossed legally only at designated border checkpoints; adjacent border zones may also be controlled.
Borders may even foster the setting up of buffer zones. A difference has also been established in academic scholarship between border and frontier, the latter denoting a state of mind rather than state boundaries.