noun
turned-down collar; lapel
Refers to a collar that is folded down, as on a jacket, coat, or shirt. Often used in clothing descriptions.
このジャケットは折り襟がきれいだ。
This jacket has a nice lapel.
折り襟のシャツを着てください。
Please wear a shirt with a turned-down collar.
襟 is the general word for 'collar'; 折り襟 specifically refers to a folded-down style.
Compound of 折り (ori, 'folding') + 襟 (eri, 'collar').