Schengen refers to the EU passport-free zone that covers most of the European countries. It’s the largest free travel area in the world.
The Schengen visa is the most common visa for Europe. It enables its holder to enter, freely travel within, and leave the Schengen zone from any of the Schengen member countries. There are no border controls within the Schengen Zone. However, if you are planning to study, work, or live in one of the Schengen countries for more than 90 days, then you must apply for a national visa of that European country and not a Schengen Visa.