Smooth section of recital, e.g. at opera (6)
I believe the answer is:
legato
'smooth' is the definition.
(musical term)
'section of recital e g at opera' is the wordplay.
'section of' says the answer is hidden in the clue.
'LEGATO' is hidden within 'recital e g at opera'.
(Other definitions for legato that I've seen before include "Smoothly, musically speaking" , "Smoothly (musical)" , "In music, the opposite of staccato" , "In a smooth and flowing manner (music)" , "Smoothly (mus.)" .)