pussy lips; labial folds
Slang/vulgar term for the labia minora or vaginal folds. The literal gloss 'labial folds' reflects the anatomical meaning of 膣襞.
I saw '膣襞' in online slang, but it's not a word you'd normally use.
Mixed kanji-katakana spelling; ヒダ is a common rendering of 襞.
Compound of 膣 (vagina) and 襞 (fold). The reading ちつひだ follows standard on-kun mixing.