Abortion vs. miscarriage

I’m having a hard time understanding this.. someone I know just miscarried her baby in her 2nd trimester . She’s saying that her miscarriage is an abortion. I always thought miscarriage and abortion were two completely different things. Why why would the medical community refer to miscarriage as an abortion? What do you understand is the definition of miscarriage? What is your understanding of the definition of abortion? (I’ve looked them up in the dictionary and that wasn’t helpful to me.)