The most common and most likely answer to this crossword clue is the 3 letter word XXX
I've seen this crossword clue in The Guardian
X
X
X
Buddy explains!

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 XXX mean?
XXX noun- An abbreviation for kisses, usually placed at the end of a letter, often placed alongside ooo, or in a text message.