Seniors' dances (5)
I believe the answer is:
proms
'seniors' dances' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for proms that I've seen before include "Sir Henry Wood's creation" , "London summer music series" , "Henry Wood concerts" , "World's largest classical music festival, held annually (inf)" , "Classical music performances, in short, some of the audience stand" .)