Refers to the small hole at the end of a sewing needle through which thread passes. Also used metaphorically for a very narrow opening or difficult passage.
It's difficult to thread a needle.
He passed the exam by the skin of his teeth (lit. as if passing through the eye of a needle).
Standard kanji spelling.
Variant using 孔, which also means hole; less common than 穴.
Compound of 針 (needle) + の (possessive particle) + 穴 (hole), literally 'needle's hole'.