Here is what the internet says:
"[A] simple net used to cover headgear. Adornments such as pearls and jewels added in 15th century."
"A lacy-looking, knitted or crocheted ‘net’ that holds the hair back"
"A band for the hair, once worn by unmarried women in Scotland as the badge of virginity; an ornamental hairnet supporting the back of a woman's hair ..."
"Snood is a puzzle video game created in 1996 by David M. Dobson. "
...okay, maybe the last one doesn't apply to my kind of snood. :)
My snoods are crocheted. Technically, crocheted snoods aren't "period" because crochet didn't really exist until the 19th century. They would have been made out of cloth or knitted.
Snoods are very useful, even in modern settings. Sometimes I try on a snood for size and find myself wearing it for a few hours because it keeps my hair out of my face better than a ponytail would. Snoods work well with short hair, because they make it look like you have longer hair, but at the same time they can do wonders for long hair and keeping it out of your way.
Even though they were mostly worn in "ancient times," you can still see them around...