Music starts with standard keys always (3)
I believe the answer is:
ska
'music' is the definition.
(I've seen this before)
'starts with standard keys always' is the wordplay.
'starts with' says to take the initial letters.
The initial letters of 'standard keys always' is 'SKA'.
(Other definitions for ska that I've seen before include "Music genre" , "Jamaican music style" , "Dancehall music" , "Noted genre" , "Jamaican music, forerunner of reggae" .)