Axure RP is a computer program that helps people make pretend websites or apps. It's kind of like playing dress up with a doll, but for websites. You can use it to make pretend buttons and menus that you can click and play with.
It's special because you can also make the pretend website or app work almost like a real one. You can make the buttons take you to different pages, and you can put in pretend forms for people to type information into.
Lots of grown-ups use Axure RP because it's really helpful when they are designing a real website or app. They can show what it will look like and how it will work before they actually make it. It helps them make sure it's what they want before they spend a lot of time and money building it for real.