The setter is on public transport, producing bit of poetry (6)
I believe the answer is:
iambus
'poetry' is the definition.
(I know that iambus is a type of poetry)
'the setter is on public transport producing bit' is the wordplay.
'the setter' becomes 'I' (the person who set this crossword).
'is on' means one lot of letters go next to another.
'public transport' becomes 'bus' (bus is a kind of public transport).
'producing bit' becomes 'am' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'bus' after 'am' is 'ambus'.
'i'+'ambus'='IAMBUS'
'of' is the link.
Can you help me to learn more?
(Other definitions for iambus that I've seen before include "Metrical unit of two syllables" , "Type of metrical unit in a poem" , "Metrical foot" , "poetic form" .)