from qt assistant:
The rect property equals QRect(0, 0, width(), height()).
This property holds the geometry of the widget relative to its parent and excluding the window frame.

example:
suppose a pushbutton is in a mainwindow:
geometry() QRect(90,50 121x91)
size() QSize(121, 91)
rect() QRect(0,0 121x91)
width() 121
height() 91

please see the doc first.