So, that ginormous pixellated white/black boxed X...

I have my drawing mode set to > Compact Normal. I notice when I am navigated to a screen which has less than four adjacent screens (the row of screens starting at 0x80 notwithstanding), a ginormous pixelated white/black boxed X fills the "adjacent screen" row and/or column to indicate that the adjacent screen doesn't exist because it's off the edge of the map. There are also single-tile pixelated white/black boxed X's covering non-adjacent 8-connected non-existent screens. See example when navigated to screen 0:

http://zcguides.celestialrealm.net/_...-interface.png

Is there an official names for this feature? What should I call it when communicating with other questmakers? Map edge barrier? What about when the adjacent screen does exist, adjacent screen tiles?

According to Etc->Options->Settings, it appears to be called Invalid Data BG. It need not be X Out - Static and Checkerboard are also available.