A poem Stein drunkenly set in South Africa (7)
I believe the answer is:
sestina
'a poem' is the definition.
(I've seen this before)
'stein drunkenly set in south africa' is the wordplay.
'drunkenly' indicates anagramming the letters.
'set in' is an insertion indicator.
'south africa' becomes 'sa' (abbreviation).
'stein' anagrammed gives 'estin'.
'estin' put into 'sa' is 'SESTINA'.
(Other definitions for sestina that I've seen before include "Bit of poetry" , "Form of poem" , "Highly structured poem of 39 lines" , "Old verse form" , "poetic structure" .)