Well. according to wikipedia...
Although the definition of sustainable development (above), given by the Brundtland Commission, is frequently quoted, it is not universally accepted and has undergone various interpretations. Definitions of sustainability may be expressed as statements of fact, intent, or value with sustainability treated as either a "journey" or "destination." Where we are now, where we need to be going, and how we are to get there are all open to interpretation and will depend on the particular context under consideration.
This difficult mix has been described as a dialogue of values that defies consensual definition. Sustainability has been regarded as both an important but unfocused concept like "liberty" or "justice" and as a feel-good buzzword with little meaning or substance. The idea of sustainable development is sometimes viewed as an oxymoron because development inevitably depletes and degrades the environment. Consequently some definitions either avoid the word developmentand use the term sustainability exclusively, or emphasise the environmental component, as in "environmentally sustainable development."
The dimensions of sustainability are often taken to be: environmental, social and economic, known as the "three pillars" These can be depicted as three overlapping circles (or ellipses), to show that they are not mutually exclusive and can be mutually reinforcing.
While this model initially improved the standing of environmental concerns, it has since been criticised for not adequately showing that societies and economies are fundamentally reliant on the natural world. According to English environmentalist and author Jonathon Porritt, "The economy is, in the first instance, a subsystem of human society ... which is itself, in the second instance, a subsystem of the totality of life on Earth (the biosphere). And no subsystem can expand beyond the capacity of the total system of which it is a part."
For this reason a second diagram shows economy as a component of society, both bounded by, and dependent upon, the environment. As the American ecological economist Herman Daly famously asked, "what use is a sawmill without a forest?"
The concept of living within environmental constraints underpins the IUCN, UNEP and WWF definition of sustainability: "improving the quality of human life while living within the carrying capacity of supporting eco-systems."
The Earth Charter goes beyond defining what sustainability is, and seeks to establish the values and direction needed to achieve it: "We must join together to bring forth a sustainable global society founded on respect for nature, universal human rights, economic justice, and a culture of peace. Towards this end, it is imperative that we, the peoples of Earth, declare our responsibility to one another, to the greater community of life, and to future generations."
The next section traces the evolution of thinking about sustainability in human history.