Indirect abortion is when a woman needs a medical treatment to save her life, but that treatment unexpectedly causes the death of her unborn baby.
Here's an example:
Let's say a pregnant woman goes to the hospital because she has a dangerous infection in her uterus. The doctors know that if they don't treat the infection quickly, the woman could die. But the medication they have to give her to treat the infection is also known to harm developing babies. So, the doctors have to give the medication to the woman to save her life, even though it might unintentionally cause harm to the baby.
In this situation, the doctors aren't actively trying to end the pregnancy. They're only trying to save the mother's life. It's an indirect result that the pregnancy ends because of the treatment.
So, to sum it up, indirect abortion is when a medical treatment is necessary to save a woman's life, but it unintentionally causes the death of her unborn baby.