Final answer:
The expulsion of a fetus before 20 weeks of gestation is referred to as a miscarriage, which is a spontaneous termination of pregnancy.
Step-by-step explanation:
The term for the expulsion of the fetus before 20 weeks of gestation is known as a miscarriage. A miscarriage typically happens very early in the pregnancy when the fetus cannot develop properly, and the body naturally terminates the gestation. This is a spontaneous termination of pregnancy, as opposed to a voluntary termination, which is referred to as an abortion. It's important to note that a fetus is considered viable and can survive outside the uterus with medical care, starting around 23 to 26 weeks.