Sustainability (or a sustainable society) is seen as one of the pillars of Biosphere Reserves in the UNESCO programme. 
"Sustainability" in this context implies quite specifically ecological sustainability, and the South African constitution has the same requirement.

Sustainability recognises that -

• the maintenance of healthy ecosystems and natural resources are preconditions for human wellbeing.
• there are limits to the goods and services that can be provided.

In other words, ecological sustainability acknowledges that human beings are part of nature and not a separate entity. Sustainable development is the process that is followed to achieve the goal of sustainability.

When development is intended, the selection of development options must allow for appropriate and justifiable social and economic goals to be achieved, based on the meeting of basic needs and equity, and all of that, without compromising the natural system on which it is based.