Spot musical instrument lady's abandoned (3)
I believe the answer is:
zit
'spot' is the definition.
(spot on one's body)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for zit that I've seen before include "Pimple (US)" , "Spot or pimple" , "Spot (colloq., mostly US)" .)