What is "mdi"

In graphical user interface, a multiple document interface (or MDI, acronym for Multiple Document interface) is a method of organizing graphical applications in windows residing in a single window, the main window of the application. The only exception are possible modal windows of the application.

One of the implications of this method is the lack of information about open windows: to view a list of open windows in an MDI application, the user should usually select a specific menu (as long as the application makes this menu available). On the other hand, in an application that implements a single document interface the task bar of the window manager is responsible for listing open windows.

Recently applications have added task bars embedded in MDI applications to display open windows, called tabs, forming a variant method called tabulated document interface. As opposed to traditional MDI, on a tabulated interface individual windows usually cannot be resized.