What is abortion?

Embryo: Until the third month of pregnancy the organism is callled embryo. After that point, it is called fetus.
Fetus: The organism after three months (when the major structures have formed) until birth.

"Abortion is the removal or expulsion of an embryo or fetus from the uterus, resulting in or caused by its death." [1]
It means that abortion is used to remove deliberately the still living blabla or the already dead blabla (spontaneously or accidentally dead as with a miscarriage).