This term is used to describe visual items that are part of parts or cells, such as radiobuttons, checkboxes, buttons, etc. "Gadgets" are not standalone programmable objects, it is merely the term used to refer to visual objects. For example, a radiobutton is represented by an instance of the RadioButtonPartClass class and it is (visually) a gadget.
Some basic attributes of gadgets can be manipulated using an instance of the GadgetsClass class.