Parametric: (Adjective) adjustable in all dimensions. A parametric model is one that can be resized and/or distorted to suit the user's needs. If the widget has a 1 cm hole in it, you can select that hole and make it a 5 mm hole with a few clicks.
Triangular meshes (STL files) are not parametric. If you open one in blender, you can't easily resize the hole. You'd have to manually select all the points that describe the outline of the hole, and move them in towards the center a bit. And blender doesn't know where the center is, so you'd have to figure that out as well.