iOS development - Windows and Views
An iOS app is displayed using windows and views.
Windows
Windows are basically containers. Their responsibility is not to directly display content, but to manage views which directly display content. If an application supports multiple screens, separate windows might be used to manage each screen. In iOS development, the UIWindow class represents a window in the code. Once a window is created, it does not change. Only the views inside the window change, as managed by the window itself.
Views
Views draw and manage visual content, as well as providing an interface for responding to user events (such as touch events and gestures). See the UIView class.