Imagine you have some toys, but different people who want to play with you have different toys at their homes. Some have dinosaurs, some have cars, and some have dolls. But you want to play with all of them, even though you have different toys from each other.
This is what happens with computer programs, or software. Sometimes, programmers create software that only works on one type of computer, like a Windows or a Mac computer. Other people with different types of computers can't use it. This is like if you had a dinosaur toy but your friends only had car toys.
But some programmers try to make software that can work on any type of computer, no matter what toys they have. This is called cross-platform software. It's like creating a toy that can be played with by anyone, no matter what kind of toy they have at home.
This way, people with different computers can use the same software and work together, even if they have different toys. And just like how you can have fun playing with all your friends and their different toys, people can enjoy cross-platform software on their computers too.