That is the definition that we can found in some dictionary or in the net:

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet, or by its Latin name, Terra.

Home to millions of species including humans, Earth is currently the only place in the universe where life is known to exist. The planet formed 4.54 billion years ago, and life appeared on its surface within a billion years. Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land. The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist during this period. The planet is expected to continue supporting life for at least another 500 million years.

Without all this formal word the definition s simply; she is the cradle of humanity. Without her benevolence, we would be nothing. She gives us life and what do we offer in return? We pollute by our garbage as well as our greenhouse gasses...

Now I just want show you beautiful place of our mother;