Song for dance commercial (6)
I believe the answer is:
ballad
'song' is the definition.
(I know that ballad is a type of song)
'dance commercial' is the wordplay.
'dance' becomes 'ball' (ball is a kind of dance).
'commercial' becomes 'ad' (abbreviation for advertisement).
'ball'+'ad'='BALLAD'
'for' acts as a link.
(Other definitions for ballad that I've seen before include "Poem telling a story" , "Song type" , "A simple or old song" , "romance" , "Folk song" .)