handbook vs reference book

handbook and reference book both are nouns.

Word	Noun	Adjective	Verb	Adverb
handbook	Yes	No	No	No
reference book	Yes	No	No	No

As nouns, reference book is a hypernym of handbook; that is, reference book is a word with a broader meaning than handbook:

handbook: a concise reference book providing specific information about a subject or location
reference book: a book to which you can refer for authoritative facts

Other hypernyms of handbook include book of facts, reference, reference work.

handbook (noun)	reference book (noun)
a concise reference book providing specific information about a subject or location	a book to which you can refer for authoritative facts