folio vs flyleaf

folio and flyleaf both are nouns.

Word	Noun	Adjective	Verb	Adverb
folio	Yes	No	No	No
flyleaf	Yes	No	No	No

As nouns, flyleaf is a hyponym of folio; that is, flyleaf is a word with a more specific, narrower meaning than folio:

folio: a sheet of any written or printed material (especially in a manuscript or book)
flyleaf: a blank leaf in the front or back of a book

Other hyponyms of folio include interleaf, page.

folio (noun)	flyleaf (noun)
a book (or manuscript) consisting of large sheets of paper folded in the middle to make two leaves or four pages	a blank leaf in the front or back of a book
a sheet of any written or printed material (especially in a manuscript or book)
the system of numbering pages