Socks that go past the knee, and reach up to the thigh. Sometimes used as a term for thigh high stockings, which are thinner amd sheerer fabric. Thigh highs are worn with skirts and shorts, often with converse or knee boots. Thigh highs are considered sexy, as they often reveal only a portion of the leg. Not to be worn by people who can't brave knee socks.
Guy 1: Damn, did you see Stacy today?
Guy 2: No. What about her
Guy 1: She wore these white socks. They were up to her thigh, and she had these short shorts, and it was HOT.
Guy 2: Thigh high socks? I gotta see that.