defining sustainability

so today i was thinking about sustainability and how it is defined. 

 it is defined as the sustainable development is to conserve, preserve and maintain resources without compromising the  needs of future activity terms in the social, environmental and economic factors of society.  

 what i find hard to understand with the definition is the fact they have to use the words "sustainable development".  

this source, an extract from the World Commission on Environment and Development. this is where the word "sustainability" has been shaped by. to be honest i can't see how sustainbility - the ideology- be defined through ' sustainable develeopment'. this is because i see sustainable development as the ideas of sustainability been put  into practise . 
what i will agree is putting in the social, economic and environmental factors because they do change the idea of sustainability.
in the end i am just one person can't change the definition. although i wish i could. maybe i'm wrong but currently don't see it. maybe because i narrowed down sustainability to a simplistic definition-the ideology to conserve , preserve, endure and maintain resource activity without compromising the future's needs in terms of economic, social and political factors.