As the eco-living movement gets more mainstream, sustainable is quickly becoming one of the most buzzworthy adjectives. The word refers to a material resource that is harvested and used so that it is renewable and not permanently depleted, while "sustainable living" is lifestyle that doesn't deplete non-renewable resources.
Fossil fuels, for instance, are not sustainable, because there are only finite amounts of them. Solar power, however, is a sustainable energy source, since it is renewable. Similarly, bamboo (pictured) is more sustainable than oak, because it grows very rapidly and can quickly be replanted.