Okay kiddo, so you know how sometimes there are hot bubbles in a pot of water when you're making spaghetti? Well, imagine there's a really really BIG pot of water under the ground in Iceland that's always hot, like a volcano. This big pot of hot water is called a "mantle plume" and it makes magma (molten rock) that can sometimes come up to the surface and make new land.
So, the Iceland Plume is basically just this big pot of hot water that's always bubbling under Iceland. It's been there for millions of years and it's what gives Iceland all its volcanic activity and hot springs. Sometimes the magma that comes from the plume can cause earthquakes and volcanic eruptions, which can be dangerous but also really cool to see!
But don't worry, Iceland is really good at keeping everyone safe and they have lots of experts who study the plume and make sure everyone stays out of harm's way. Plus, it's also what makes Iceland such a unique and special place to visit!