Ruined area between Truro and Slough (7)
I believe the answer is:
trashed
'ruined' is the definition.
(I've seen this in another clue)
'area between truro and slough' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'between' indicates putting letters inside.
'truro' becomes 'tr' (I can't explain this - if you can you should believe this answer much more).
'and' means one lot of letters go next to another.
'slough' becomes 'shed' (both can mean to discard something).
'tr'+'shed'='trshed'
'a' inserted inside 'trshed' is 'TRASHED'.
Can you help me to learn more?
(Other definitions for trashed that I've seen before include "Criticised" , "completely taken apart" , "Destroyed" , "Vandalised" .)