Socks that are knee-height, or just below knee-height.
Despite the name, kneehighs are usually slightly shorter than knee-height, usually ending a few inches below the knee, or at around 3/4 calf height.
If they're completely below shin-height, they're ankle socks.
See over-kneehighs for thighhighs that reach just above the knee. See knee boots for knee-length boots.
This tag implicates socks (learn more).