Okay kiddo, do you know what a satellite is? It's like a big metal ball or box that's way up high in the sky. Some of them help us watch TV shows or use the internet, and some of them help us use our cell phones when we're in places that don't have regular phone towers.
The International Mobile Satellite Organization, or IMSO for short, is an organization of countries that work together to make sure all those cell phone satellites work properly. They also make rules to keep everyone safe and make sure the satellites don't hurt the Earth by crashing into it or causing problems with the environment.
IMSO is like a teacher for all the countries that use those cell phone satellites. They help check that all the rules are being followed, and they help make sure that everyone shares the satellites fairly.
So basically, it's a group of countries working together to make sure everyone has access to safe and reliable cell phone service, no matter where they are in the world, thanks to those helpful satellites in the sky!