A snood is a woman's hairnet or fitted head covering. You've probably seen paintings of nineteenth century women wearing snoods.
A snood covers and pulls back the hair, much like a hairnet worn by a restaurant worker. But while a hairnet is functional, meant to keep strands of hair from ending up in customers' food, a snood is ornamental, more like a hat or scarf. It's uncommon to see women wearing snoods these days, but they show up all the time in nineteenth century art. The root of snood is the Old English snod, "hair ribbon."