medley vs piece of music

medley and piece of music both are nouns.

Word	Noun	Adjective	Verb	Adverb
medley	Yes	No	No	No
piece of music	Yes	No	No	No

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

medley: a musical composition consisting of a series of songs or other musical pieces from various sources
piece of music: a musical work that has been created

Other hypernyms of medley include composition, musical composition, opus, piece.

medley (noun)	piece of music (noun)
a musical composition consisting of a series of songs or other musical pieces from various sources	a musical work that has been created