We use the term a lot, but what does it actually mean. That depends. Most of us accept that our current lifestyle is not sustainable, with most differences of opinion being over how long a given consumption rate (or growth rate) could be sustained. Some people try to cast "sustainability" as some type of extreme ecotopia with humanity reduced to the lowest forms of hunter / gatherer society. However, there are many paths to sustainability and over a long enough time period, we will either have to consciously choose our own path to sustainability or eventually a solution will imposed on us. In some areas, this may require more technology, like wind, solar, tidal electricity generation. In other areas it may require a return to older low tech ways of production like organic farming.

I have found "Sustainability" to be a good neutral word to use in conversations when talking about a wide range of topics from fiscal policy to fossil fuel consumption. It has an intuitive logic that almost everyone can accept as "good" and everyone that our current consumption levels are not sustainable on many different levels.

Below are some different definitions that I found by doing a google search on the term "sustainable". Find the one that you think best describes sustainability or come up with your own definition.

being able to continue into the future.

The using of products of nature in a way that will not permanently destroy them for future use. Sustainable resources allow for the resources to regenerate before being used again.