Organdie is a crisp, sheer fabric made of silk or cotton. Old-fashioned, formal children's clothes with big, stiff, ruffles are often made of organdie.
Organdie is so fine that it's nearly translucent, but a special finish is usually applied to make it stiff and prevent wrinkling. Light summer dresses are sometimes made of organdie with a lighter finish, while fancy organdie curtains tend to be much stiffer. The word's origin, beyond the French organdi, is a bit of a mystery, though it may stem from Organzi, an Uzbek city that was once a textile center.