Mini Velos ("velo" means "bike" in French) are bicycles that typically have 20" or smaller wheels. Such small-wheeled bikes have less inertia than typical 26" or 700C bike and are therefore easier to accelerate from a stationary position. They are also more responsive to the riders' steering and tend to maneuver better in small lanes and tight corners. Since they are lighter and smaller than typical bikes, they can be easily kept within apartments.
Choose a Mini Velo if you need a bike that is lighter, more agile, and where you need to save some storage space and do not need to cover very long distances.