A world's fair is like a really big party where people from all over the world come together to show off cool things they've made or found. People set up big buildings called pavilions where you can go inside and learn about different countries, inventions, and ideas. At the world's fair, you can also see fun attractions like rides and games. It's a big celebration of all the amazing things people can do and create, and it happens every few years in different places around the world.