Okay, so let's try this.
An integro-differential equation is like a really complicated math sentence that tells us how something changes over time. It's made up of two parts, an "integral" and a "differential."
The integral part is like a really big math problem, where we have to add up lots of smaller math problems all at once. It helps us figure out how much of something there is, and how much it's changing.
The differential part is like a mini-math problem, that tells us how something is changing right at that moment. It's like taking a snapshot of a situation, to see how things are moving and changing at that very moment.
So, when we put these two parts together in an integro-differential equation, we get a really powerful tool that helps us understand all sorts of things, like how heat moves through a building or how water flows in a river.
It's kind of like having a special pair of glasses that lets us see things we couldn't see before. With an integro-differential equation, we can solve problems that might seem impossible at first, and learn amazing things about the world around us!