Widget is a visual component of the module, a kind of Popup that will be displayed in the room. The main task of the widget is to display the basic controls of the subdevice and to provide a module transition to the Remote control of the subdevice. For example, to control a media player, you can place a volume slider or Mute button for quick access to adjusting the volume. The weather widget can display the current weather, and the control panel will contain the weather forecast for all 5 days.
The module does not make sense without widget, because it will not have a graphical representation in the i3 lite project.