* Bunny is often used as a more informal and endearing term for a young rabbit, especially a baby rabbit called a "kit".
* Rabbit is the more formal and scientific term, encompassing all members of the Leporidae family, regardless of age.
So, technically, all bunnies are rabbits, but not all rabbits are bunnies.
It's like calling a baby "little one" instead of "child." Both terms refer to the same person, but one is more casual and affectionate.