This question seems to taunt both aspiring and experienced permies alike and most of the time the answers I hear people give fumbles the ball. At least in my opinion.
Most peoples first impression of permaculture colours all their future views of it either positively or negatively. Some enter through urban permaculture where it seems mostly like a bunch of fancy gardening techniques. Some enter from a traditional large scale agriculture background and see it as a bunch of hippy ideas without a solid business plan. Some enter it as big eyed idealists that grab onto it as a silver bullet that will hopefully save humanity, proven or not.
The honest truth is that permaculture is all of these things and none of these things. When faced with most questions, a curious person asks about how permaculture relates to their specific situation, the cliche answer tends to be "It depends". What this answer really means is that when designing using permaculture, there isn't a recipe. The more factors that are taken into account,the better design it will ultimately be.
The problem is that this answer is ultimately unsatisfying to the person that asked the question. So I've been searching for a simpler and more concise answer than just "it depends" or the alternative hour long lecture involving an extensive history lesson. What I've come up with is "It's a design philosophy that aims to reintegrate humans into their ecosystem". If I lead with that answer to what permaculture is, following up with the specific questions with "it depends" has a natural tag of "if it meets the overall goal of integrating you into an ecosystem."
Q: "Can I do or use <anything> in my permaculture design."
A: "Yes, as long as it meets the overall goal of integrating you into an ecosystem. Each designer and user of a permaculture system gets to decide what meeting that goal ultimately looks like though. Therefore, it depends"
For 500 Year Farm that means creating a successful, regenerative and ecological business I can be proud of and hand down to the next generation.