Window height used for |CTRL-F| and |CTRL-B| when there is only one window and the value is smaller than 'lines' minus one. The screen will scroll 'window' minus two lines, with a minimum of one. When 'window' is equal to 'lines' minus one CTRL-F and CTRL-B scroll in a much smarter way, taking care of wrapping lines. When resizing the Vim window, the value is smaller than 1 or more than or equal to 'lines' it will be set to 'lines' minus 1. Note: Do not confuse this with the height of the Vim window, use 'lines' for that.