sustainability - what does it mean - part 1

So sustainability has been an obsession of mine for as long as I can remember.  I've always felt that the way we live in the world was flawed, and that there was a better way.  Bias exists.  You have been warned.

I'm taking a course to expand my understanding of sustainability-the concept.  I have my answer (flawed I'm sure, and sometimes open to discussion, but not much...) but I'm trying to learn to look from a different, more global and more scientific perspective.  The course I'm taking is free, it's on the futurelearn.com site, and it has made me think.

Here's the link https://www.futurelearn.com/courses/sustainability

I'm going to, from time to time, post thoughts, ideas, and questions about sustainability.  Hope we can generate a conversation.  The course I'm taking has people from all over the world, but I have real problems with their assumptions (not the participants, the course providers... the participants seem to be drinking the cool-aid just fine.)

So, question one - What is sustainability?

Hoping you will post an answer so we can have a conversation.