I have heard both words used to refer to a book. Some sources in the internet say there is no difference.
My experience from listening to French language is that perhaps "le bouquin" is a more informal word used to refer to modern books. For instance, I have heard Olivier Roland use the word "bouquin" to refer to a book he wrote or to a book he recently read. On the other hand, during première/deuxième lecture in a church it is always "lecture du livre de...".
Is there a difference in the usage of both words? Would one of these words be used more often in a specific region/country?