Okay kiddo, sometimes things happen that are really big and don't happen every day, and we call that ir-regular activity. When we say large irregular activity, we mean something that is really huge and not normal.
It could happen in different things like your body or even the world around you. For example, some people might have a fever, which means their body temperature is really high and not normal.
In the world around us, we might experience natural disasters like big earthquakes, hurricanes or even volcanic eruptions, and those are also examples of large irregular activity.
When something like this happens, it can cause a lot of changes and can even be dangerous, and it's really important for people to pay attention and stay safe.