There is no single definition for sustainability. There are many definitions of sustainability. Presently, the field of sustainability integrates many disciplines including; economic development, the natural and built environment, energy efficiency, food systems, and social justice and equity.
Below is a collection of definitions by various authors, politicians, and professors.
The Brundtland Commission
The World Commission on Environment and Development defined sustainable development as that which "meets the needs of the present without compromising the ability of future generations to meet their own need."
"Leave the world better than you found it, take no more than you need, try not to harm life or the environment, make amends if you do."
"Then I say the earth belongs to each...generation during its course, fully and in its own right. The second generation receives it clear of the debts and encumbrances, the third of the second, and so on. For if the first could charge it with a debt, then the earth would belong to the dead and not to the living generation. Then, no generation can contract debts greater than may be paid during the course of it's own existence."
"If you get right down to it, sustainability is really the study of the interconnectedness of all things."
"Sustainable design is the careful nesting of human purposes with the larger patterns and flows of the natural world."
"The 'greatest good for the greatest number' applies to the [number of] people within the womb of time, compared to which those now alive form but an insignificant fraction. Our duty to the whole, including the unborn generations, bids us to restrain an unprincipled present-day minority from wasting the heritage of these unborn generations."