A snood is a hairnet worn by ladies. It is depicted in medieval artwork and archaeology from the 13th century onward. In period, they were made by netting and possible by crochet in very late period. A similar item, called a caul is made out of solid fabric such as linen.
Snoods are popular headwear at SCA events and Rennaisance fairs. Hair styles and hats are a complicated affair throughout much of the middle ages. A snood is something that can be purchased cheap, is easy to wear, and enhances a lady's garb. It is also a convenient medievaloid way to keep your hair out of your face when working.