Puzzle concerning coach (5)
I believe the answer is:
rebus
'puzzle' is the definition.
(type of visual puzzle)
'concerning coach' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'coach' becomes 'bus' (synonyms).
're'+'bus'='REBUS'
(Other definitions for rebus that I've seen before include "Puzzling device" , "Picture-puzzle" , "Pictorial pun - fictional detective" , "Visual pun" , "Word puzzle with pictures and letters" .)