[sukilot]

O'Reilly's in an interesting story. He became fabulously wealth by selling partly/mostly closed-source books about open-source software, in the short time-window when opens source existed while it was also possible to make money selling books (before Internet samizdat became cheap as free)

[packetslave]

WTF is a "closed-source book"?

[cujic9]

The opposite of an open source book.

I'd assume the parent is thinking of something like the "Pro Git" book, available on Github as code and licensed under creative commons. https://github.com/progit/progit2