The United States National Arboretum is a really big outdoor park with lots of trees and plants located in Washington D.C. Think of it like a big garden where you can go and look at all the pretty plants and trees.
The Arboretum was created a long time ago by the government to help people learn about different plants that are important for our environment and our daily lives. It's like a big science experiment where they grow different trees and plants to figure out how to make them grow better and help the environment.
The Arboretum has many different areas that you can explore, each with different types of plants and trees. They also have special displays that show how different types of plants are used for things like medicine and food.
If you go to the Arboretum, you can take a tour with a guide who can explain everything to you and answer any questions you have. Or you can just explore on your own and see what you find! It's a really cool place to learn about nature and see all the different plants and trees that make up our world.