revision vs piece of writing

revision and piece of writing both are nouns.

Word	Noun	Adjective	Verb	Adverb
revision	Yes	No	No	No
piece of writing	Yes	No	No	No

As nouns, piece of writing is a hypernym of revision; that is, piece of writing is a word with a broader meaning than revision:

revision: something that has been written again
piece of writing: the work of a writer; anything expressed in letters of the alphabet (especially when considered from the point of view of style and effect)

Other hypernyms of revision include writing, written material.

revision (noun)	piece of writing (noun)
the act of revising or altering (involving reconsideration and modification)	the work of a writer; anything expressed in letters of the alphabet (especially when considered from the point of view of style and effect)
something that has been written again
the act of rewriting something