kivy - kivy「インスタンス」には何がありますか? on_pressed(self, instance, pos) のように

Question

instancekivyで単語が何を意味するのか知りたいですか?

class CustomBtn(Widget):
    pressed = ListProperty([0, 0])

    def on_touch_down(self, touch):
         if self.collide_point(*touch.pos):
             self.pressed = touch.pos
             # we consumed the touch. return False here to propagate
             # the touch further to the children.
             return True
         return super(CustomBtn, self).on_touch_down(touch)

     def on_pressed(self, instance, pos):
         print ('pressed at {pos}'.format(pos=pos))
         print ('My callback is call from', instance)