What exactly is meant by "The American Dream" ?

I’ve been wondering, since I was in tenth grade in 1980 and a song was out by the Nitty Gritty Dirt Band, called, “American Dream.”

I’ve heard it used to describe Suburbia, or economic stability. Or a political promise such as ‘a chicken in every pot, two cars in every garage… all things possible for all people…’

But what is it, and what does this term mean?

A good thing or a bad thing, and no matter what you personally think of it, how do you define it?

All answers, ‘in reference to’s’ and contexts are welcome for discussion.