One of the best definitions I have encountered with regards to permaculture is that is a design process to meet human needs in a way that enhances ecosystem health, as best we can, in the circumstances which also creates a surplus for reinvestment into the system.
It is purpose-driven, goal orientated. When looking at definitions, it can come down to the difference between 'permaculture' and 'permaculture design'.
When we look around at nature, we see permacultures surrounding us. Things that are in a beautiful symbiotic relationship, the mutualism of living things showing the dynamic equalibrium, supporting each other where the system as a whole grows in wealth.
We, as designers, work with the information that we can gather around us. With other peoples designs, we can look at what other people have done in different places and look at how it relates to where we are.
The design process is about helping us to do things in a permaculture fashion - better and faster. It is interesting to see the difference between peoples various definitions of permaculture because there is always this thing of context and the importance of observing where we are.
Because unless we know where we are, we do not see what we can do.
This is one of the critical things to learn. Most people understand there is an observation phase, but we need to understand the context.
Many permaculture books and blogs are full of different tools and techniques, and this is awesome. Many people are doing amazing things with some of these tools - vast abundance in areas that defy most peoples ideas of what is possible (for example, Sepp Holtz)
The danger is that if you do not consider these more significant issues or are new to permaculture. You see various tools - Hugelculture, compost toilets, swales, solar panels, etc. and you take these things and put them in your garden, and that makes it permaculture.
Permaculture is about solving problems. While putting in a hugel bed or compost toilet may sound cool, we need to ask what problem is this solving. Is it related to temperature, water, soils etc. and how is this particular tool solving the problem. While that specific tool might work for them, will it work within my own context? Is it the right tool for the job. The learning of permaculture is not just learning the tools, but also the best way to apply them in space and place to produce a surplus.
What is a tool within permaculture? Well, anything can be, subject to context.. all tools in the toolbox.. but when you consider it is a design process that is a problem-solving approach that works at the strategic level, thus choosing the right tool for the right job, seeing someone just apply a tool because "well it is permaculture" asking what problem it is solving becomes even more critical.