Описание тега qtgui
QtGui module extends QtCore with GUI functionality. It has collection of classes useful for creating Qt based GUI applications
Prior to qt5, the Qt GUI module was the monolithic container for all things relating to graphical user interfaces in Qt, and included the Qt widget set, the item views, the graphics view framework and also printing. Starting Qt 5, these classes have been moved to the Qt Widgets module. Printing has been moved to the Qt Print Support module. Please note that these modules can be excluded from a Qt installation.
If you use qmake to build your projects, Qt Gui is included by default.
The official Qt documentation can be found here for Qt 4.8 and here for Qt 5.