Puzzle concerned with public transport (5)
I believe the answer is:
rebus
'puzzle' is the definition.
(type of visual puzzle)
'concerned with public transport' is the wordplay.
'concerned with' becomes 're' (re can mean regarding or about).
'public transport' becomes 'bus' (bus is a kind of public transport).
're'+'bus'='REBUS'
(Other definitions for rebus that I've seen before include "Word puzzle with pictures and letters" , "Word-picture puzzle" , "solver?" , "Puzzling device" , "Pun picture puzzle" .)