Sustainability has a very different signification in function of the context where it is mentioned.
In the environmental policy, sustainability (or sustainable development) generally refers to a "development that meets the needs of the present without compromising the ability of future generations to meet their own needs."
(UNFCCC glossary, http://unfccc.int/essential_background/glossary/items/3666.php, 12 March 2007)
In other contexts, such as the economy for example, "sustainable" often stands for "continuous".
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