Sustainable and self-sustainability are all terms that I've been hearing more and more about.
Off the grid, means that you have a private windmill or solar power that provides all your electricity (possibly loading specialized batteries for the cloudy or windless days.) You have a private well and septic system. Basically you could live as a hermit with modern conveniences.
Sustainable means that you have everything set up so that it can successfully continue on with little or positive impact on future generations.
Self-sustaining means that you can live off the grid and your lifestyle would end up having a positive impact on future generations. Plant your own gardens, can fruit and vegetables, or set up a year round green house.
I can't help but wonder if we are coming into a generation where the hippie communes of the 1060's are going to become the new fad. Hmmm?