The introitus is an entrance that goes into a canal or hollow organ. Introitus is another name for the vaginal orifice.
introitus has been used for classifying uterine prolapse
1st degree prolapse-cervix is in the vagina
2nd degree-cervix at the level of the introitus
3rd degree-cervix comes out of the introitus
procidentia-the uterus also comes out of the introitus