So, you know how mommy takes medicine to prevent her from getting pregnant? That medicine has something called progesterone, which helps keep a baby from growing in her tummy.
Well, antiprogestogens are like the opposite medicine! They go into mommy's body and stop the progesterone from working. This can be helpful if mommy does not want to be pregnant anymore and needs to have an abortion.
Antiprogestogens also have other uses in medicine, like helping to treat certain types of cancer or controlling heavy menstrual bleeding.
So basically, antiprogestogens are medicine that stop mommy from having a baby or can help with other health problems.