The type A visa (Airport Transit Visa) allows citizens of non-Schengen states to transit through or wait for their connecting flight in the international zone of an airport located in a Schengen country. It is compulsory for those travelling from a non-Schengen country to another non-Schengen country and who have to connect flights in the airport of a Schengen country. The holder of a type A visa is not allowed to enter the said Schengen country. The type B visa relates to journeys lasting fewer than five days has been replaced by type “C” with the condition “transit".
The short stay Schengen visa is the most common one. It is issued by the visa services (embassies, consulates, appointed external providers) of a country belonging to the Schengen area. It allows the holder to stay or travel freely in the Schengen area for less than 90 days over a 180 day period. According to the purpose of your trip, the short-stay category C Schengen visa can be : a single-entry, a double-entry or a multiple-entry. The national visa is the type D long-stay Schengen visa. It is mandatory for any foreigner wishing to study, work or live in a Schengen country for longer than 90 days (up to 1 year).
You need to apply for a Schengen Visa if you intend to visit one or more European countries in the area for any of the following reasons: Tourism and recreation, business purposes, visiting friends or family, cultural and sporting events, airport and seafaring transit visits, official visits, medical treatment, short-term study, and research purposes. Depending on your reasons for visiting the Schengen Area countries and the frequency of your visits, the Schengen consulate can issue you a single, double, or a multiple-entry visa - valid for 90 days. However, if you are a frequent traveler, you may apply to obtain a multiple-entry Schengen Visa valid for up to five years. On each visit, you will only be able to stay within the Schengen Area for up to 90 days in a 180-day period.