The most common and most likely answer to this crossword clue is the 3 letter word REC
I've seen this crossword clue in Independent
R
E
C
Buddy explains!

The straight part
We know that "park" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case park = rec.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 REC mean?
REC noun- A recommendation or suggestion.
- A recreation ground.
- To recommend.
- To record.
- Any activity, such as play, that amuses, diverts or stimulates.
- The process of recreating something.
- The result of this process.
- For, or relating to, recreation.