Nature, in the broadest sense, is equivalent to the Planet Terra aka Gaia or Earth, physical world, or material world. "Nature" refers to the phenomena of the physical world, and also, to life in general. It ranges in scale from the subatomic to the cosmic.
In the series, Terra is the planet where all of the characters were born, and Nature is the guardian of the balance of life, death, and the evolution of species.
So far, nothing has been established completely as to whether Terra has a conscience, but according to the words of the witches, Terra is the source of magical powers, and according to Sheila, Terra, also known as Nature, has plans for the species, given to understand that Nature is a form of basic and primitive consciousness