The Schengen Visa in image

In practical terms, a Schengen Visa is a secured label sticked on a page of a passport.

The Schengen Visa and Schengen States

It allows the holder to enter in the 24 Schengen States for a uninterrupted stay on:

• a one entry visa or for several consecutive stays
• a multiple Entry Visa which total term cannot exceed 3 months per semester from the date of first entry.

More information on Wikipedia