Lean Publishing is the act of self-publishing a book while you are writing it, evolving the book with feedback from your readers and finishing a first draft before optionally using the traditional publishing workflow.
While Lean Publishing is a new term, and this is its first formal definition, the ideas behind Lean Publishing have emerged over the past decade from a number of sources. These sources include the Lean Startup community, the "beta book" or "early access" programs of a few savvy publishers, my own experience in writing and self-publishing a successful technical book, and the blogging community, especially authors such as Jason Fried and David Heinemeier Hansson who have pioneered evolving blog content into bestselling books.
The Lean Publishing process can be used by authors of almost any type of book--as we'll see later, there is even historical precedent it can work for novels--but it is especially suited for authors of non-fiction books. This is because non-fiction books, and especially technical books, benefit the most from early exposure to their readers.
As we'll see in the case studies, this was true for my book, Flexible Rails: it earned me over $13,000 in royalties as a self-published technical book before it was even finished. To date, I have earned over $48,000 in total royalties from Flexible Rails, and one of the most interesting things is that over 70% of that has been from PDF book sales.