The essence of the term sustainable is “that which can be maintained over time.” By implication, this means that any society that is unsustainable cannot be maintained for long and will cease to function at some point.
Unfortunately, in recent years the word sustainable has become widely used to refer merely to practices that are reputed to be more environmentally sound than others. Often the word is used so carelessly as to lead some environmentalists to advise abandoning its use.The Post Carbon Reader Series: Foundation Concepts
Nevertheless, the concept is indispensable and should be the cornerstone for all long-range planning.
What Is Sustainability?
By Richard Heinberg