gtk-widget-destroy (widget)

widget -- a gtk-widget object

Destroys a widget. When a widget is destroyed, it will break any references it holds to other objects. If the widget is inside a container, the widget will be removed from the container. If the widget is a toplevel, derived from the gtk-window class, it will be removed from the list of toplevels, and the reference GTK holds to it will be removed. Removing a widget from its container or the list of toplevels results in the widget being finalized.

In most cases, only toplevel windows require explicit destruction, because when you destroy a toplevel its children will be destroyed as well.