Senior moment? (4)
I believe the answer is:
prom
'senior moment?' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for prom that I've seen before include "Classical music concert for which part of the audience stands" , "Formal dance at the end of school year" , "BBC summer concert" , "Short walk" , "Albert Hall concert" .)