A government places an endorsement in a passport—or issues an electronic authorization—permitting a foreign national to enter for a stated purpose and duration. That endorsement is a visa. It is a core instrument of border control.

Visa rules differ by nationality, destination, and purpose of travel. Some travelers may enter many countries without a visa; others must apply in advance with documentation, fees, and sometimes interviews. Overstaying a visa can lead to fines, deportation, or future entry bans.

Electronic visas and visa-on-arrival systems have simplified procedures for many tourist nationalities. Requirements can change with little notice, so checking official sources before travel remains essential. A valid visa does not guarantee admission; border officers retain final authority.

Without the right visa, even a fully paid trip can end at the immigration desk.