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1.
When something is noteworthy.
1st person: "That kid just spat fire."
2nd person: "That's BOOK!"
by themerrypranksters May 03, 2008

Words related to that's book

awesome cool fresh great super sweet thats book that's cool
 
2.
Something that is so interesting/intriguing, that conventional sayings can't fully depict the awesomeness that was witnessed.
Speaker One: She lifted a house with one finger.
Speaker Two: That's book.
by trophy2 February 06, 2010