Defined:
It has been oft stated that there are as many definitions of permaculture as there are practitioners. This isn't meant to dilute the vitality of permaculture, but to acknowledge that there is no dogma when it comes to its practice.
From David Holmgren: "'Consciously designed landscapes which mimic the patterns and relationships found in nature, while yielding an abundance of food, fibre and energy for provision of local needs'...the use of systems thinking and design principles that provide the organising framework for implementing the above vision." From Permaculture: Principles and Pathways Beyond Sustainability (2002)
Of course, there are many, many definitions of permaculture. Every person that practices permaculture develops her or his own language to express that practice.
Here is another comprehensive definition.