The number you see below is your external or public IP address. It's like the main entrance to your internet connection, the address the rest of the internet sees you coming from.
Why is this useful?
Sometimes websites or services need to know your general location (like for showing local news or setting the right language). Your IP address helps them do that (though it's not exact!). It can also be used for things like, advertisers, online gaming, analytics filtering or security purposes.
Don't worry, it's generally not something you need to know every day! This page just makes it easy to find out if you ever need it.