What is the meaning of Urogenital_sinus?

A body part present in the embryos of mammals during development of the urinary and reproductive systems that gives rise to the bladder, urethra, lower vagina, prostate gland, vulval vestibule, vestibular glands, and bulbourethral glands.

An internal structure where the vagina and urethra open into in many female mammals.

Source: wiktionary.org