Class in area of study backed by corporation (7)
I believe the answer is:
stratum
'class' is the definition.
(I've seen this before)
'area of study backed by corporation' is the wordplay.
'area of study' becomes 'arts' (as opposed to the sciences).
'backed' says the letters should be written backwards.
'by' means one lot of letters go next to another.
'corporation' becomes 'tum' ('corporation' is a humorous term for stomach fat).
'arts' reversed gives 'stra'.
'stra'+'tum'='STRATUM'
'in' is the link.
(Other definitions for stratum that I've seen before include "Layer (of rock)" , "Social class - level" , "Bed of sedimentary rock" , "rock band" , "(Geological) layer" .)