You use sustainable to describe the use of natural resources when this use is kept at a steady level that is not likely to damage the environment (Collins Cobuild English Dictionary in my electronic dictionary =D)
While studying architecture, professors talked a lot about sustainable development, plan, method or system. That means, when you design buildings or plan cities, your design or plan should be developed without any problems. Actually, the word 'sustainability' is derived from 'maintain' and 'endure' (wikipedia). In this sense, a sustainable city and architecture should endure changes occurred over time. So, those aims to meet environmental needs and human needs, even meet future generation's needs.
This image have a meaning the artist expressd below.
This is the best visualization. It shows that, in the ultimate analysis, the transition from consumerism to sustainability must happen in human minds and hearts before it can happen at any level - local, national, or global.
This model suggests the additional (and critical) insight that the transition is contingent on gender equality and cross-gender solidarity. Sustainable development will require the collaboration of all men and women of good will.
The transition from homo economicus to homo ecologicus requires gender equality, because the ecological mindset cannot take root and grow as long as humans are engaged in any form of domination; and patriarchy is the most pervasive structure of domination.
(http://www.pelicanweb.org/solisustv07n03supp1.html)
