I'd have to go look at my book... I have one too. ( several actually) never use it but I have them.....It appears to be a ruffler.........
another great you tube!!
http://www.youtube.com/watch?v=cZLFeBNapIk
I wish I had known and used this foot ( that I already owned!!) when I did my Grandaughters nursery.. my dtr wanted ruffles on EVERYTHING!@!!! sigh....