While I agree with the Agile Manifesto I've never been great at defining "Agile" in terms of it.
As time goes by I find the manifesto increasingly looks like a historic document. It was written in response to the problems in the software industry at the turn of the millennium - problems I recognize because I was there. I worked on the Railtrack privatization, I'm ISO 9000 certified, and produced so much paper you needed a train to move it. I worked at Reuters as they destroyed their own software capability with a CMM stream roller.
The manifesto is a little like the Magna Carta or the US Constitution, you sometimes have to read into it what would fit your circumstances. It was written about software and as we apply Agile outside of software you have to think, "what would it say?" the same way the US Supreme Court looks at the Constitution and interprets what it would say about the Internet
Perhaps a more interesting question than "What is Agile?" is "Where does Agile apply?" or, even more interesting, "Where does Agile not apply?"
One can argue that since Agile includes a self-adaptation mechanism (inspect and adapt) - or as I have argued, Agile is the embodiment of the Learning Organization - it can apply to anything, anywhere. Similarly, it has universal applicability and can fix any flaws it has.
Of cause it's rather bombastic to make such an argument and quite possibly anyone making that argument hasn't thought it through.
So the definition of "Agile" becomes important - and since we don't have one, and can't agree on one we're in a rather tricky position.
Increasingly I see "Agile" (and so some degree Lean too) as a response to new technologies and increasing CPU power. Software people - who had a particular problem themselves - had first access to new technologies (programmable assistants, email, instant messenger, wikis, fast tests and more) and used them to address their own issues.
The problems are important. Although people have been talking about "Agile outside of software development" for almost as long as agile software development it has never really taken off in the same way. To my mind, that's because most other industries don't have problems which are pushing them to find a better way.
As technologies advance, and as more and more industries become "Digital" and utilize the same tools software engineers have had for longer than those industries, these industries increasingly resemble software development. That means two things: other industries start to encounter the same problems as software development but they also start to apply the same solutions.
Software engineers are the prototype of future knowledge workers.
Which implies, the thing we call Agile is the prototype process for many other industries
"Agile outside of software" becomes a meaningless concept when all industries increasingly resemble software delivery.