Okay kiddo, so a mobile network is like a big spider web that connects lots of phones and computers together. And usually, the people who make the spider web decide how it works and what it can and can't do.
But with a software-defined mobile network, the spider web can change and adapt more easily because the people who made it can change or "program" it using a computer.
It's kind of like playing with Lego blocks. You can build different shapes and designs by snapping blocks together or taking them apart, and the same goes for a software-defined mobile network. The people who made it can add or remove parts, and even change how the parts work together, just like with Lego blocks.
This can make the mobile network faster, more reliable, and more flexible to do different things depending on what people need. It's kind of like having a "smart" spider web that can change to help people better.