Festival displays its charms (9)
I believe the answer is:
christmas
'festival' is the definition.
(I know that Christmas is a type of celebration)
'displays its charms' is the wordplay.
'displays' indicates anagramming the letters (I've seen 'displayed' mean this (letters displayed in another way)).
'its'+'charms'='itscharms'
'itscharms' with letters rearranged gives 'CHRISTMAS'.
(Other definitions for christmas that I've seen before include "Yule, Noel" , "The festive season harms tics, oddly" , "See 14 Across" , "Nativity feast" , "The present day" .)