noun
ruff; ruffled collar
A collar with many small folds or pleats, often seen on historical European clothing or formal wear.
あの肖像画の人物は大きな襞襟をつけている。
The person in that portrait is wearing a large ruff.
襟 is a general collar; 襞襟 specifically refers to a ruffled or pleated collar.
Compound of 襞 (ひだ, 'pleat') and 襟 (えり, 'collar').