Area behind factory occupied by church organ (8)
I believe the answer is:
placenta
'organ' is the definition.
(I have seen 'temporary organ' mean 'placenta' so perhaps 'organ' could also mean 'placenta')
'area behind factory occupied by church' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'behind' is a charade indicator (letters next to each other).
'factory' becomes 'plant' (a manufacturing plant).
'occupied by' indicates putting letters inside (inserted letters occupy or enter the word).
'church' becomes 'ce' (abbreviation for Church of England).
'plant' going around 'ce' is 'placent'.
'a' after 'placent' is 'PLACENTA'.
(Other definitions for placenta that I've seen before include "primary food supplier" , "Source of nourishment for embryo" , "temporary organ" , "Organ feeding a foetus" , "21 that feeds the embryo" .)