Sustainable society refers to a society which is in balance with the earth's ecosystems, and which could be indefinitely maintained. In simpler terms, sustainability mean making decisions that do not knowingly conflict with the future. The notion of sustainability has not been necessary until the recent past, for it is only in the twentieth century that we have clearly demonstrated that humankind can significantly alter the individual and combined ecosystems of the Earth.
Sustainability is best seen in terms of time. We all practice short term sustainability by avoiding actions which could cause injury or harm; we call it "common sense". Looking farther ahead in time, we think of "planning" as the means to assure goals, though the goals themselves usually have less "long term common sense". But few individuals think farther ahead than five or ten years, and most people assume and trust that groups of humans (large businesses and governments) are doing that for them. And only a very few human entities look farther into the future than ten or twenty or thirty years.
Sustainability expands the accessibility of the future and encourages, even demands, that individuals practice probing the future to a far greater distance than thirty years. Sustainability would in fact suggest that to look forward any less than perhaps seven generations, or about two hundred years, would be foolish, and that looking beyond seven generations would be prudent.
We cannot, of course, know specifics of the future even a few years away. But we can know a lot more about the future than we care to admit, and the first step to do so is to begin to think with a perspective which admits a reality of two hundred years in the future. People who specialize in looking ahead, or have a high degree of interest in the future, call themselves futurists, a term coined about one hundred years ago referring to a French art movement.
Here's some links to make you think.