Arbor Day is an annual event that is celebrated in many countries around the world to promote the planting and care of trees. It is typically held on the last Friday in April in the United States, and on various dates in other countries depending on the best time for tree planting in that region. The first Arbor Day was held in Nebraska in the United States in 1872, and the holiday has since spread to many other countries. On Arbor Day, people often plant trees, participate in tree-related activities and events, and learn about the importance of trees and the role they play in the environment.