A visa is a conditional authorization granted by a country to a foreigner, allowing them to enter, remain within, or to leave that country.
Visas typically include limits on the duration of the foreigner's stay, territory within the country they may enter, the dates they may enter, the number of permitted visits or an individual's right to work in the country in question. Visas are associated with the request for permission to enter a country and thus are, in some countries, distinct from actual formal permission for an alien to enter and remain in the country.
In each instance, a visa is subject to entry permission by an immigration official at the time of actual entry, and can be revoked at any time. A visa most commonly takes the form of a sticker endorsed in the applicant's passport or other travel document.
Historically, immigration officials were empowered to permit or reject entry of visitors on arrival at the frontiers. If permitted entry, the official would issue a visa, when required, which would be a stamp in a passport. Today, travellers wishing to enter another country must generally apply in advance for what is also called a visa, sometimes in person at a consular office, by mail or over the internet. The modern visa may be a sticker or a stamp in the passport, or may take the form of a separate document or an electronic record of the authorization, which the applicant can print before leaving home and produce on entry to the host country. Some countries do not require visitors to apply for a visa in advance for short visits.
Some countries require that their citizens, as well as foreign travellers, obtain an "exit visa" to be allowed to leave the country.Uniquely, the Norwegian special territory of Svalbard is an entirely visa-free zone under the terms of the Svalbard Treaty.
Some countries—such as those in the Schengen Area—have agreements with other countries allowing each other's citizens to travel between them without visas. The World Tourism Organization announced that the number of tourists requiring a visa before travelling was at its lowest level ever in 2015.