"The word permaculture was coined by Bill Mollison and myself in the mid-1970’s to describe an integrated, evolving system of perennial or self-perpetuating plant and animal species useful to man.
A more current definition of permaculture, which reflects the expansion of focus implicit in Permaculture One, is ‘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.’ People, their buildings and the ways in which they organise themselves are central to permaculture. Thus the permaculture vision of permanent or sustainable agriculture has evolved to one of permanent or sustainable culture."
David Holmgren (co-creator of Permaculture)
The above paragraphs are probably the most concise definitions I have found for Permaculture. I could spend a lot of time recreating a much more detailed definition, but there is no point in reinventing the wheel. Following are links to two other in depth explanations of Permaculture:
Link to Wikipedia article: http://en.wikipedia.org/wiki/Permaculture
Link to Holmgrem’s 23 page PDF: http://www.holmgren.com.au/DLFiles/PDFs/Essence_of_PC_eBook.pdf