At the moment, third eye can be used for "any artwork depicting a character with more than one eye. The third eye does not have to be part of the body."
This statement is extremely vague, and leads to wildly different interpretations:
There's the classic third eye on the forehead (post #4686498), and then there are less uncommon things such as reiuji_utsuho's chest eye (which is sometimes more of a jewel than an actual organic eye), or even the satori sisters' big detached eye.
The latter three specifically are used as example in the wiki, which makes me wonder whether they should get their own tags, or if third eye should become an umbrella tag for various kinds (this way the "classic" third eye can be put in forehead_eye or something like that).
EDIT: Apparently ibaraki_douji's eye on the forehead, which i believe is painted, also counts as third eye.
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