This is a challenge cache where you can only log the cache as a "Found It" if you have found and list 20 or more caches with the word "park" or "parks" in their titles.

As you probably have inferred from the title, this challenge relates to parks. If you have not found enough park(s) geocaches, you may still find the cache, but you may not log it as a find. Instead, you may write a note saying you found it and once you complete the task, you can change the note to a "Found It."

If you go to "play" on the geocaching website, you can search caches found by you with specific words/titles. There is a filter to the right of the search box where you can limit the search to words/titles of geocaches that you have already found.