The most common and most likely answer to this crossword clue is the 11 letter word CONCERTGOER
I've seen this crossword clue in The Times
C
O
N
C
E
R
T
G
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More clues leading to the result CONCERTGOER
Buddy explains!
The straight part
We know that "One might see prom" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one might see prom = concertgoer.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CONCERTGOER mean?
CONCERTGOER noun- A person who attends a concert, especially one who attends concerts often