Christie, I was wondering what AAR meant, too. I think it's something like how much wear you can get out of one item due to how many different ways you can wear it.
An open vamp or "low" vamp means that more of the top of your foot is exposed. For instance, these shoes have a low vamp, because if you put them on, you would see a lot of the top of your foot--the toe box is shorter:
http://www.zappos.com/n/p/dp/39104382/c/90.html
These on the other hand, have a high vamp (yeah, I think they may be slippers as well):
http://www.zappos.com/n/p/dp/35385752/c/621.html
If you're wearing a skirt, dress, or walk shorts, shoes that have a low vamp are good because they don't disturb the vertical line you're creating by breaking up your leg too soon. I've found that you can wear shoes that are close to your skin color, or metallics like gold or silver with higher vamps and still get away with it while wearing skirts/dresses/walk shorts. It helps if they are a sandal though, and have other openings to show off your foot.
Hope that makes sense.