A cervix is the neck or a part of an organ resembling a neck.
When people speak of the cervix, they are usually talking about the cervix uteri, or the neck of the uterus, which is the lower part from the lower os of the uterus to the external os. It is rounded and protrudes slightly into the vagina. It is about an inch long and is penetrated by the cervical canal through which childbirth takes place.