Code mobility is when computer programs (or "code") can move around from one device to another. Imagine you have a Lego car you made and you can take it apart and move it to another room or even share it with your friends. Code mobility works the same way.
Let's say you wrote a cool game on your computer. Normally, the game will only work on your computer, but with code mobility, it can be moved to other devices too. For example, you could move the game to your friend's computer or even to your phone so you can play it on the go.
Code mobility is like sharing toys, but instead of sharing physical objects like Lego cars, we are sharing computer programs. This makes it easier for people to access and use the same programs on different devices without having to rewrite the code.