Festival in overseas territory (6)
I believe the answer is:
easter
'festival' is the definition.
(Christian festival)
'in overseas territory' is the wordplay.
'in' indicates a hidden word.
'EASTER' is hidden within 'overseas territory'.
(Other definitions for easter that I've seen before include "Church festival" , "Time to celebrate" , "Annual religious festival" , "Resurrection festival" , "See art at this time of year" .)