Musical work penned by Byron downloaded (5)
I believe the answer is:
rondo
'musical work' is the definition.
(type of musical composition)
'penned by byron downloaded' is the wordplay.
'penned by' says the answer is hidden in the clue.
'RONDO' is hidden in the letters of 'byron downloaded'.
(Other definitions for rondo that I've seen before include "Donor (anag) - piece of music" , "Repetitive musical form" , "Music form with repeating theme" , "Musical composition with a recurring theme" , "Musical form with recurrent theme" .)