A book is a perfect example of that.
The prime example of passive income used here is patio11's Bingo Card Creator.
One also could say that in traditional investing, the upfront work is the research work to find right index funds or buying property in real estate investing. They might be less work than writing a book, but revenues e.g. from passive index fund investing are also significantly less than from writing a book, if your starting capital is small.
This is the key point. In absolutes there is no such thing as passive income. Anything will take at least 1s of effort, and $0.001 of capital. The spirit of the term, is income that is heavily skewed towards being generated from assets rather than effort.
A new book is the edge case. While making money off IP is generally the perfect example of passive income. Quitting a job to become an author, is not. There is an implied lack of effort and cost in the question. Additionally, and importantly, there needs to be a sense of "free" in there.
The prototypical case:
- [bust your ass at work] >> [get evened out with paycheck] >> ["free!" passive income from savings]
New book case:
- [bust your ass writing] >> [nothing, world still owes you] >> ["free?" passive income from book IP]
Until the "nothing" gets filled in with the equivalent of a salaried wage, I'm not a fan of calling it "passive income".
