Mould spreading after dropping contents in sections (7)
I believe the answer is:
modular
'in sections' is the definition.
(divided into modules or sections)
'mould spreading after dropping contents' is the wordplay.
'spreading' is an anagram indicator.
'dropping contents' means to remove the middle letters.
'after' with its middle taken out is 'ar'.
'mould' is an anagram of 'modul'.
'modul'+'ar'='MODULAR'
(Other definitions for modular that I've seen before include "Made from detachable pieces" , "Made of units" , "Built from separate units" , "in several parts" .)