This page allows you to control whether axes lines are drawn around the plot or not. In general this isn't very useful for spectral plots (when the outer border lines and axes are coincident), but it does allow you to draw the axes inside the display area and position where these are drawn, so you can define an arbitrary origin. Useful effects can then be obtained using grid lines.
The Log X: and Log Y: options are the same as those shown in the Limits pane.