Alright kiddo, so when a baby is growing inside a mommy's tummy, sometimes something goes wrong and the baby can't grow like it's supposed to. When that happens, the mommy's body can "resorb" the baby. That means it kind of eats it up and gets rid of it so that it doesn't cause any harm.
Think of it like when you eat some food that your tummy doesn't like, your body gets rid of it and takes what it needs from the food. Mommy's body does the same thing with a baby that can't grow properly.
It's important to remember though that fetal resorption isn't something that happens often and it's not because mommy didn't take care of herself or the baby. Sometimes things just don't work out, but mommy's body knows what to do to keep her safe and healthy.