some book; a book on the subject
Used when referring to an unspecified book, often implying that the information is found in some written source. The phrase 物の本によると is common.
According to some book, this plant is said to be medicinal.
General plural sense, often used in a slightly literary or old-fashioned way to refer to books collectively.
He reads books whenever he has free time.
Compound of 物 (もの, 'thing') + の (possessive particle) + 本 (ほん, 'book'). The exact historical derivation is uncertain, but the phrase has been used since at least the Edo period to refer to books in a general or unspecified way.