It is a document issued by a country to a person to formally ask the traveling country for permission, with a specific reason for a stipulated amount of time. All the countries have their own VISA laws and it is up to the country to allow a traveler to allow him/her or not. A visa does not guarantee entry, a person may also may also be rejected after getting permitted. A VISA can be of many types like business , tourist, study, visitor or work.