The lowdown on class (5)
I believe the answer is:
genre
'class' is the definition.
(genre can mean a class or type)
'the lowdown on' is the wordplay.
'the lowdown' becomes 'gen' (gen can informally mean information).
'on' becomes 're' ('on' can be mean 'with reference to').
'gen'+'re'='GENRE'
(Other definitions for genre that I've seen before include "Literary type, species" , "Green (anag)" , "Artistic or literary category" , "expressive style of music" , "Brand" .)