The most common and most likely answer to this crossword clue is the 9 plus 5 letter word CLASSICAL MUSIC
I've seen this crossword clue in The Guardian
C
L
A
S
S
I
C
A
L
M
U
S
I
C
More clues leading to the result CLASSICAL MUSIC
Buddy explains!

The straight part
We know that "this/this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case this/this = classical music.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.