window-min-height

window-min-height is a variable defined in `window.el'.
Its value is

4

Documentation:
The minimum total height, in lines, of any window.
The value has to accommodate one text line, a mode and header
line, a horizontal scroll bar and a bottom divider, if present.
A value less than `window-safe-min-height' is ignored. The value
of this variable is honored when windows are resized or split.

Applications should never rebind this variable. To resize a
window to a height less than the one specified here, an
application should instead call `window-resize' with a non-nil
IGNORE argument. In order to have `split-window' make a window
shorter, explicitly specify the SIZE argument of that function.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.1 of Emacs.