The following is a description of the Frame Widths page of the Custom Settings panel for a Basic Window, from the INT Archicad Library.
If Uniform Frame Width is checked (either on this tab page, or on the Frame and Sash tab page), then you set a single width value for all sides of the frame.
If you uncheck Uniform Frame Width, you can set varying width values for the sides, (as for a complex-shaped window).