interfenestration 

The space between two windows.

The interfenestration was two inches/three meters/a mile/pi radians.

interfenestration by echjman May 30, 2005

Interpenetration 

Apparently it's when parts of geometry appear to be clipping through other parts.

Mostly on games.

Timmy: Hey look, that door just went through that chair when i opened it!
Tod: Ahh, thats just good old Interpenetration son, get used to it.

Interpenetration by [Cyanide] September 12, 2004