An Airport Transit Visa is a type of visa that allows travelers to pass through the international transit area of an airport without entering the country. This visa is typically required for passengers who have a layover in a country where they need to change flights but do not plan to leave the airport. Travelers must apply for an Airport Transit Visa in advance, as it is not issued upon arrival. The requirements may vary by country, so it is essential to check the specific regulations of the country where the layover occurs before traveling.