Dang 裆 is the joint of the two legs of the trouser, and in English should be both the front rise and back rise of the trouser as show in the following link :
https://www.3sixteen.com/pages/measuring-guide-jeans
It is a mistake to translate Dang as crotch as in Wikipedia:
https://en.wikipedia.org/wiki/Open-crotch_pants
Most people from China knew about the traditional Kai Dang Ku 开裆裤 (open pants) for kids and the position of the Dang.