Noun
entrance or opening to a hollow organ or tube (especially the vaginal opening)
Source: WordNetthe introitus of the vagina Source: Internet
The definition of birth as defined in the bill was that once any part of the body had passed beyond the introitus, it is considered a birth. Source: Internet
Vaginal opening and hymen The vaginal opening (orifice or introitus) is at the caudal end of the vulva, behind the opening of the urethra, resting at the posterior end of the vestibule. Source: Internet