Okay kiddo, so do you know what a glacier is? It's a big huge chunk of ice that's formed over thousands of years from snow that never melted.
Now, there is an area in the Irish Sea (a big body of water between Ireland and the UK) where scientists believe that there might have been a glacier a long time ago.
This glacier was made up of ice that was slowly flowing and sliding over the sea floor. It probably moved very slowly, kind of like how a snail moves, over thousands and thousands of years.
But, we can't see the glacier anymore because it has melted away. Scientists have found some rocks and other evidence that tells us that there might have been a glacier there a long time ago. They study and learn about these things so that they can understand how the world works and how it changes over time.