The cervix is the neck of the uterus. This is the place where the uterus joins with the top end of the vagina. It is normally blocked by a muscosal plug which helps to prevent infection, and which has to evacuated before the birth process can begin.
The PAP-smear as we know it is an invention of Dr. G.N. Papanicolaou, 1883-1962, an American of Greek birth, the father of cytopathology. He first published a large series of cases in "Diagnosis of uterine cancer by the vaginal smear" (Papanicolaou & Traut, 1943) The sampling technique has hardly changed ever since.