toccata vs piece of music

toccata and piece of music both are nouns.

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

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

toccata: a baroque musical composition (usually for a keyboard instrument) with full chords and rapid elaborate runs in a rhythmically free style
piece of music: a musical work that has been created

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

toccata (noun)	piece of music (noun)
a baroque musical composition (usually for a keyboard instrument) with full chords and rapid elaborate runs in a rhythmically free style	a musical work that has been created