fit-frame-to-buffer-margins

fit-frame-to-buffer-margins is a variable defined in `window.el'.
Its value is

(nil nil nil nil)

Documentation:
Margins around frame for `fit-frame-to-buffer'.
This specifies the numbers of pixels to be left free on the left,
above, on the right, and below a frame fitted to its buffer. Set
this to avoid obscuring other desktop objects like the taskbar.
The default is nil for each side, which means to not add margins.

The value specified here can be overridden for a specific frame
by that frame's `fit-frame-to-buffer-margins' parameter, if
present. See also `fit-frame-to-buffer-sizes'.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.4 of Emacs.