Xenopregnancy is when an animal of one species carries and gives birth to offspring of a different species.
Imagine you have a cat and a dog. Normally, they can't have babies together because they are different species. But scientists have been studying how to make them have babies together by taking the cat's egg and putting it into the dog's womb. Then, the dog carries the baby cat inside her and gives birth to it.
It's like if your mom had a baby for your neighbor who couldn't have babies. She carries the baby inside her, but it's not her own baby – it belongs to the neighbor.
Xenopregnancy is still really new and scientists are still figuring out if it's safe and how to make it work for more than just cats and dogs.