banana skin vs banana peel

banana skin and banana peel both are nouns.

Word	Noun	Adjective	Verb	Adverb
banana skin	Yes	No	No	No
banana peel	Yes	No	No	No

As nouns, banana skin and banana peel are synonyms defined as:

banana skin and banana peel: the skin of a banana (especially when it is stripped off and discarded)

banana skin (noun)	banana peel (noun)
the skin of a banana (especially when it is stripped off and discarded)	the skin of a banana (especially when it is stripped off and discarded)