Electronic flower festival (6)
I believe the answer is:
easter
'festival' is the definition.
(Christian festival)
'electronic flower' is the wordplay.
'electronic' becomes 'e' (as in e-mail or e-books).
'flower' becomes 'aster' (type of flower).
'e'+'aster'='EASTER'
(Other definitions for easter that I've seen before include "Card, egg or Island" , "8 9 [PACIFIC ISLAND]" , "Resurrection festival" , "- Day; - bunny" , "Christian feast of the Resurrection" .)