Puzzle about public transport (5)
I believe the answer is:
rebus
'puzzle' is the definition.
(type of visual puzzle)
'about public transport' is the wordplay.
'about' becomes 're' (regarding).
'public transport' becomes 'bus' (bus is a kind of public transport).
're'+'bus'='REBUS'
(Other definitions for rebus that I've seen before include "In Edinburgh, busy" , "Pictorial teaser" , "Picture and word puzzle" , "Problem" , "Enigmatic representation" .)