A visa is an authorization given by the foreign affairs or the Immigration authority of a  country for a foreign citizen to enter its territory and to remain there for a limited duration. Each country typically attaches various conditions of their visas, such as duration of stay, the territory covered by the visa, dates of validity, single visit or multiple visit, etc. Visas are associated with the request for permission to enter a country, and are thus, for some countries, distinct from actual formal permission for    an alien to enter and remain in the country. In any event, a visa is subject to permission of an immigration official at the time of actual entry, and can be revoked at  any time.

Most visas are issued by the Embassy of a country, but in some cases the Visas needed to obtained from the country directly also there are countries which issues the visa only by a sponsorship.