> 
> >From the description, I would bet it's 'no changes are allowed to this
> feature' and 'changes are allowed to this feature'.  I wonder if it's
> possible to drag-and-drop things onto the button to add them when it's
> in the unlocked state?
>

It must be something like a tiling/appearence lock for X windows.

Find out what "window manager" you are using, and look at its documentation.