[spacemanspif]

It's a popular term around here. Basically just a sharp edge that enables clean separation instead of the air trying to wrap around the radius of the edge and create turbulence. MetroMPG made some nice ones for the back bumper of his Civic. I guess in a way it's like a miniature box cavity just like the little spoilers on most new cars are mini kamm backs. It's the designers adding little bits that still look good while performing a specific function.