piece of paper vs sheet of paper

piece of paper and sheet of paper both are nouns.

Word	Noun	Adjective	Verb	Adverb
piece of paper	Yes	No	No	No
sheet of paper	Yes	No	No	No

As nouns, piece of paper and sheet of paper are synonyms defined as:

Other synonyms of piece of paper include sheet.

piece of paper (noun)	sheet of paper (noun)
paper used for writing or printing	paper used for writing or printing