noun
The part of a shirt, coat, kimono, jacket, or similar garment around the neck; also covers lapels and collar-like neckbands.
シャツの襟が少し汚れている。
The collar of the shirt is a little dirty.
寒いのでコートの襟
It was cold, so I turned up the collar of my coat.
noun
nape of the neck; scruff of the neck
Limited or old-fashioned as a standalone body-part word; modern Japanese more often uses うなじ, 首筋, or 襟首 for the nape or scruff.
古い用法では、「襟」が首の後ろ、つまりうなじを指すことがある。
In older usage, 襟 can refer to the back of the neck, that is, the nape.