Mobile internet is when you can use the internet on your phone or tablet, even when you're not at home or near a Wi-Fi connection. Just like how you can watch videos or play games on your computer at home with Wi-Fi, you can also do these things on your phone or tablet when you're out and about.
Your phone or tablet uses something called a SIM card to access the internet. The SIM card is a little piece of plastic that goes into your phone and helps it connect to the mobile internet. It's kind of like a key that unlocks the internet for your phone.
When you're using the mobile internet, your phone or tablet sends and receives information through something called a cellular network. This means that there are big towers all around that help your phone connect to the internet. Just like how you need to be near a Wi-Fi router to use Wi-Fi at home, you need to be near one of these towers to use the mobile internet when you're out and about.
The mobile internet is great because you can use it almost anywhere, even on a car ride or when you're on vacation. However, it's important to remember that sometimes it can cost money to use the mobile internet a lot, especially if you use a lot of data (which is like the amount of internet you use). So be sure to ask an adult before using too much mobile internet!