Okay, so imagine you are playing with your toys and then you get very sleepy. You want to take a nap, right? Just like you need to sleep to rest your body, sometimes big places like countries need to rest too. This is what we call "hibernation" - it's when something takes a very long rest.
One of these big resting places was called "Hibernia" a long time ago. Hibernia was actually the name the Romans gave to a big island that we now call Ireland. Just like how you have a name, Hibernia was a way for the Romans to call this big island.
Speaking of Romans, the Roman Empire was a very, very big place that had a lot of different people and places in it. Think of it like when you go to school and there are a lot of classrooms. Each classroom has different kids and a different teacher. The Roman Empire was like a school with a LOT of classrooms.
The Roman Empire was around a long time ago - even before your mommy and daddy were born! They were really good at building things and they built a lot of big buildings, like the Colosseum that you may have seen in pictures, and they had great soldiers who could fight really well.
The Roman Empire was so big that they even had people visit Hibernia/Ireland, but they didn't stay there for too long. Hibernia was a bit too far away for them to visit often.
So, to sum it up, Hibernia was the name the Romans gave to the big island now known as Ireland and the Roman Empire was a really big place a long time ago with a lot of people and places in it.