'Howl!' — poem recited as a series of lines (3,4)
I believe the answer is:
bar code
'series of lines' is the definition.
(pattern of lines encoding information)
'howl poem recited as a' is the wordplay.
I cannot quite understand how this works, but
'poem' could be 'ode' (ode is a kind of poem) and 'ode' is found within the answer.
'a' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for bar code that I've seen before include "Pattern of stripes containing information for computer processing" , "Stock item marker" , "that needs scanning" , "Machine-readable arrangement of parallel lines on product" , "Brocade (anag.)" .)