Knee socks are a kind of long socks or hosiery. How long exactly depends on the context:
- In Japanese, it refers to thigh-high socks or stockings (aka thighhighs) and over-knee socks. The main tags on Pixiv are ニーソックス and ニーソ. Also, Western fandom uses the word mostly like this as well.
- Traditionally, in the West, it refers to socks that reach almost up to the knee, i.e. knee-highs.
Overview
Since the turn of the century, knee socks have become extremely popular among characters in the pursuit of the "Absolute Territory".
Usage Notes
In Western fandom, there can be some ambiguity because "knee socks" can refer to both over-knee socks and knee-highs, but generally the latter is much more commonly called/tagged "kneehighs" or "high socks".
In Japanese, "knee socks" originally meant knee-highs as well, but there really isn't any overlap anymore and they now unambigiously mean thighhighs/overknees.
Note that knee socks are specifically socks or non-sheer stockings. "Thighhighs" or "overkness" can refer to any piece that is thigh/overknee-length, including boots, sheer stockings, leg warmers, etc.. So if its long socks, it's recommended to tag in English with "kneesocks"
