Ran raves in New Year's annual celebration (11)
I believe the answer is:
anniversary
'annual celebration' is the definition.
'ran raves in new year's' is the wordplay.
'new' indicates anagramming the letters.
'year' becomes 'y'.
'ran'+'raves'+'in'='ranravesin'
'ranravesin' anagrammed gives 'anniversar'.
'anniversar'+'y'='ANNIVERSARY'
(Other definitions for anniversary that I've seen before include "special event" , "Eg, a birthday" , "Yearly commemoration" , "Celebration" , "Day marking a past event" .)