Sustainable development is the development that meets the needs of the present without compromising the ability of future generations to meet their own needs.
It means that we don't affect the resources at the extent that they cant be used anymore. We reduce the emission of greenhouse gases. We stop deforestation. We stop extracting minerals so much that they can't renew themselves. We reduce pollution. We clean our surrounding, oceans and the atmosphere. All this is done while also meeting the needs of the present.