Borders are usually defined as geographical boundaries, imposed either by features such as oceans and terrain, or by political entities such as governments, sovereign states, federated states, and other subnational entities. Political borders can be established through warfare, colonization, or mutual agreements between the political entities that reside in those areas.

An open border is a border that enables free movement of people between jurisdictions with no restrictions on movement and is lacking substantive border control. A border may be an open border due to intentional legislation allowing free movement of people across the border, or a border may be an open border due to a lack of legal controls, a lack of adequate enforcement or adequate supervision of the border. An example of the former is the Schengen Agreement between most members of the European Economic Area. An example of the latter has been the border between Bangladesh and India, which is becoming controlled. The term "open borders" applies only to the flow of people, not the flow of goods and services, and only to borders between political jurisdictions, not to mere boundaries of privately owned property.