page number vs folio

page number and folio both are nouns.

Word	Noun	Adjective	Verb	Adverb
page number	Yes	No	No	No
folio	Yes	No	No	No

As nouns, page number and folio are synonyms defined as:

Other synonyms of page number include pagination, paging.

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