Permaculture is a term first coined by Bill Mollison and David Holmgren in the 1970s. It is a contraction of the words "permanent" and "agriculture" and refers to the use and design of land in a sustainable manner, modeled after nature. For anyone who is interested in living a more green lifestyle, Permaculture is a valuable subject to learn and practice.
Here is a good YouTube video that gives a little introduction to the topic. There are lots of good videos on the subject on the internet, and I'll be posting some more soon.