A more thorough explanation:

Partial-birth abortion is a type of abortion where a viable fetus is partially delivered before being destroyed. Abortion is the artificial termination of a pregnancy to destroy an embryo or fetus.

According to the Supreme Court, a woman has the right to choose to end her pregnancy before viability, which is when the fetus could live independently of its mother. However, after viability, the state can regulate or prohibit abortion unless it is necessary to preserve the life or health of the mother.

Examples of other types of abortion include:

• Induced abortion: An abortion purposely and artificially caused either by the mother herself or by a third party.
• Late-term abortion: An abortion performed during the latter stages of pregnancy, usually after the middle of the second trimester.
• Spontaneous abortion: The spontaneous expulsion of an embryo or fetus before viability; also known as a miscarriage.
• Therapeutic abortion: An abortion carried out to preserve the life or health of the mother.

Partial-birth abortion is controversial because it involves a viable fetus being partially delivered before being destroyed. Some argue that it is a form of infanticide, while others argue that it is necessary in certain medical situations.