A Schengen visa is an authorization issued by a Schengen Member State for:

a) transit through or an intended stay in the territory of the Schengen Area for a duration of no more than three months in a six-month period (from the date of first entry into the territory of the Schengen Area) or

b) transit through the international transit areas of airports of the Schengen Member States.

The EU Visa Code (Regulation (EC) No. 810/2009 of the European Parliament and the European Council of 13 July 2009) forms the legal basis for the Schengen visa.

Source: Europa. Zusammenfassung der EU Gesetzgebung, Ihr Europa, edited