It is a day designed to inspire awareness and appreciation for the Earth's environment. This means that everyone should protect the planet we live in. It is celebrated in many countries every year.
Nowadays this day is celebrated all around the world, but it was "invented" by an American Senator Gaylord Nelson.
Visit this site in Wikipedia and find out more about this day, the activities and the ideas people defend.
http://en.wikipedia.org/wiki/Earth_day#Earth_Week
