Would this dress be suitable for a semi-formal school dance?

Besides prom this is the first non casual dance our school has ever had. Therefore I'm not exactly sure how fancy it should be. I really want to wear this dress a href="http://www.promgirl.com/shop/dresses/viewitem-PL556971" rel="nofollow"http://www.promgirl.com/shop/dresses/vie…/a and heels but I don't want to be overdressed. Also please explain if you don't mind what semi-formal is.