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6.
a) A set of prescribed standards or rules on which decisions are based: runs the company by the book.
b) Something regarded as a source of knowledge or understanding.
c) The total amount of experience, knowledge, understanding, and skill that can be used in solving a problem or performing a task: We
used every trick in the book to finish the project on schedule.
d)Informal. Factual information, especially of a private nature: What's the book on him?
Idioms:
in (one's) book
In one's opinion: In my book they both are wrong.
(above from dictionary.com)