International mobile subscriber identity

Imagine you have a special number that you use to make phone calls and send text messages on your cell phone. This number is called your "international mobile subscriber identity" or "IMSI" for short.

Just like how your name identifies you, your IMSI identifies your phone and connects you to your mobile network so you can use your phone to call and text other people.

Your IMSI is special because it's not only used in your home country but it also works when you travel to other countries. This way, even if you're not in your home country, you can still call and text just like you would normally.

So, in summary, an IMSI is a special number that identifies your phone to your mobile network and works internationally, allowing you to use your phone to communicate no matter where you are in the world.