The word permaculture, coined by Australians Bill Mollison and David Holmgren during the 1970s, is a portmanteau of permanent agriculture and permanent culture.

The term permaculture initially meant "permanent agriculture" but this was quickly expanded to also stand for "permanent culture" as it was seen that social aspects were an integral part of a truly sustainable system. Mollison and Holmgren are widely considered to be the co-originators of the modern permaculture concept.

Permaculture is an ecological design system for sustainability in all aspects of human endeavor. It teaches us how build natural homes, grow our own food, restore diminished landscapes and ecosystems, catch rainwater, build communities and much more.

 
Modern permaculture is a system design tool. It is a way of
   1. looking at a whole system or problem
   2. seeing connections between key elements (parts)
   3. observing how the parts relate,
   4. planning to mend sick systems by applying ideas learnt from long-term                                           sustainable working systems.

Permaculture is loosely defined as a lifestyle philosophy.

Holmgren's 12 design principles
David Holmgren has developed 12 design principles for permaculture:
   1. observe and interact
   2. catch and store energy
   3. obtain a (sustainable) yield
   4. apply self-regulation and accept feedback
   5. use and value renewable resources and services
   6. produce no waste
   7. design from patterns to details
   8. integrate rather than segregate
   9. use small and slow solutions
   10. use and value diversity
   11. use edges and value the marginal
   12. creatively use and respond to change

For more information see: http://permaculture.org