"Wool socks" refers to a type of socks made from the wool of sheep. They are warm and cozy, and are commonly worn to keep feet comfortable during cold weather. Full definition
Note that when wearing rubber boots in snow it is an urgent need to wear wool socks in the boots. (highlatitudestyle.com)
Boots by the way are warm but good pair of wool socks doesn't hurt. (sorel.com)
I have worn those winter hiking boots only 3 - 4 times this season so far, sometimes for warmth because I can wear thick wool socks with them. (joy.lookfab.com)