Puzzle concerning public transport (5)
I believe the answer is:
rebus
'puzzle' is the definition.
(type of visual puzzle)
'concerning public transport' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'public transport' becomes 'bus' (bus is a kind of public transport).
're'+'bus'='REBUS'
(Other definitions for rebus that I've seen before include "Pictorial word puzzle" , "solver?" , "Word puzzle involving pictures" , "Puzzling symbols, etc" , "Pictorial teaser" .)