This is the best explanation I have seen online, with pictures:
http://corneredcat.com/basics/stance.aspx
That website, while designed to introduce women to the world of shooting and self-defense, it a great resource for ANYONE looking for information.
I'm glad she showed a photo with the "Faux Isosceles".
I see lots of ladies do that at the range, especially at CCW qualifying. Good to know there's a name for it.