Wikipedia defines grass as, "The common word that generally describes monocotyledonous green plants." And we all know what monocotyledonous means... right?
Is it natural?
Oh heck yes. Good ol' mother nature has spread her goodness around the earth and it's called "Grass". Don't trust me? Well, go ahead, eat it! You won't die...or will you? (;
Why is it important?
More than a fifth of the earth is covered by grasslands, like for example, the prairies of north America and the Savannahs of Africa. These grasslands provide precious food for huge grazing herds of animals.
Who eats it?
A lot of animals in this world consume grass. The examples below are the zebra, wildebeest, and giraffe. Giraffes don't eat it very often but when they do they have to spread their legs to get their head down far enough to eat the yummy goodness.