You may have seen this type of sock in various viral videos. Unlike some viral videos (I'm looking at you, crystals from charcoal and peanut butter, busted by the Mythbusters) these socks are the real deal.
Yoga socks are heel- and toe-less to let you grip your yoga mat while keeping your feet warm. Also great for martial artists.
I currently have a small stash of a wool/ bamboo blend avalable to use.