Puzzle about transport (5)
I believe the answer is:
rebus
'puzzle' is the definition.
(type of visual puzzle)
'about transport' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'transport' becomes 'bus' (busing is a kind of transporting).
're'+'bus'='REBUS'
(Other definitions for rebus that I've seen before include "Visual pun" , "Pictorial teaser" , "Enigmatic representation" , "Pun picture puzzle" , "Word puzzle with pictures and letters" .)