A visa is an authority issued by the Embassy/Consulate of a country that permits a traveler to visit that particular country. The majority of visas are stamped inside your passport. (A small number of visas are either separate document to be carried with the passport or issued electronically.) Visas are issued with specific limitations regarding purpose of visit, length of stay, validity of visa, etc... Some countries do not require a visa or do not require a visa in some situations, such as a result of reciprocal treaty arrangements. The possession of a visa is not in itself a guarantee of entry into the country that issued it, and in certain cases a visa can be revoked at any time.