I would say it's for a small dance perfomance. I've been dancing not for so long (less than 2 years). And our school organizes small dance show for our relatives and friends (but not only newbies will take part in this perfomance, those who dance for real long will also participate to demonstrate the beaty of the "dance world").
Although we are not real professionals we still want to look and dance as good as possible :) The school doesn't have any rules concerning dresses' look (not all the people would want to spend much money for the real professional dance dress especially if they dance only for a year).
So as I assume there are no general rules about costumes - only some competitions can estabilish obligatory limits.
Thank you for your answers!
Dana.