I've been discussing with a friend about Earth Day and at a certain point came out the question 

> 
> What do you call "nature"?
> 
> 
> 

He said that he considers "nature" basically all matter, including plastics and all kind of man-made materials.

I said that as far as I understand, "nature" is the ensemble of all Earth's ecosystems, thus if something is not part of an ecosystem, it is not "nature".

Is there an official definition of what is considered to be "nature"?
If yes, what is it? If no, is there a reason?