It's just one of the 3 Creative Feet (See "Creative Feet" thru Google, and it will go to their website), and a friend has it on her machine she uses for all of her quilting. It has a white side that sticks out from the stainless foot and presses against the edge of the quilt square, so then the needle is just 1/4" away from the edge if you set your needle on the lefthand side.
It seems to guide a longer piece of the fabric through the machine.
Lulie