Shadoan - I agree that sometimes "sustainable" can just be a greenwashed term for a slightly less hideous form of exploitation of nature. Certainly it's being used to put a positive and green spin all kinds of practices that are neither sustainable nor ecologically sound.

What it means, in my own life and I'm making no personal claim to any kind of lifestyle high ground, is doing my best to minimize my footprint and not be wasteful, and doing my best to live in a way that supports practices that can be maintained with minimal negative impact upon people and nature. So, eating food from farms that doesn't destroy the land being farmed (and animals being bred for food) and locally when possible. Growing some of my own food. Using public transport and a bike instead of driving a car. And so on. I'm certainly not self sufficient, but that's not my goal since I think mutual communal sufficiency is actually more sustainable in the long run considering the world population.

In the big picture, sustainable practices mean practices that don't destroy ecosystems. It's a pretty complex issue in many ways even though it can seem very simple and is in other ways. I'm not convinced we haven't gone past the tipping point - but I do believe the planet will right itself even if it becomes inhospitable to humans. So, in some ways, sustainability is about trying to keep the planet hospitable to sustaining human life in the future.

All creatures manipulate the environment to some extent in order to live. I agree with you that a "green" road through he jungle is not sustainable. To leave nature alone entirely is also not sustainable, as we are not able to sustain ourselves without taking some things from nature. I would caution against saying we must "leave nature alone", as it implies that we are not nature. It is true that we have created many things that I would not consider a part of nature in their obvious macro form, but we, as a biological species, can never really remove ourselves from nature; we ARE nature. In an interest in bringing our living back into harmony with the ecosystem, we must chose our words carefully to keep this important point in mind.

Sustainable in it's simplest definition means that which may continue at the current rate or level. This certainly would not make laying down any type of road sustainable, yet it does allow for using materials in nature at a rate that may be replaced and thus provide continuous sustenance and material support. I had a great environmental ethics teacher years ago that suggested that it was sustainable to harvest redwood trees, if we simply allow the 1000 years after the harvest of each tree to allow it to replace itself.

Bringing these 2 thoughts together, it is important to understand, even at the most basic level, the interconnected nature of the ecosystems in which we are members. We are a part of that system, which means we rely of other components of nature for our well-being. Additionally, we must take care to keep the system healthy and thriving so that we may continue to make our living with Gaia's great gifts, thus never altering nature so much that the system is harmed or changed.

To me sustainability means living life in a way that promotes and encourages the growth and development of all forms of life around us. creating appropriate technologies that creates symbioses with the environment.
I think that we can box that term in to mean life in an eco-friendly manner, but I feel that sustainability has as much to do with our interactions with other humans as well as our interactions with this wonderful planet that we live with.