A visa is the confirmation provided by a country that an individual is allowed to enter, stay in, or transit through it. It is usually issued as an entry visa; some countries also require exit visas or a visa for traveling the country itself.

In the German Residence Act (AufenthG), a visa (§ 6 AufenthG) is defined as one of several possible residence titles. These titles are generally required for citizens from non-EU countries wishing to enter or stay in Germany. According to European Regulation (EC) No. 810/2009, a visa can be issued as a Schengen visa – for a stay in the Schengen Area for up to three months within a period of six months - or as an airport transit visa. Longer stays in Germany require a national visa. The following residence titles can be issued: residence permit, EU Blue Card, settlement permit, or EC permanent residence permit.

Source: AufenthG, Wikipedia (only available in German), edited