Green open spaces? (5)

I believe the answer is:

holes

I'm a little stuck... Click here to teach me more about this clue!

'spaces?' is the definition.
(hole is a kind of space)

I can't explain the rest of the clue.

(Other definitions for holes that I've seen before include "Scrapes" , "Empty spaces" , "Apertures" , "Openings" , "Cavities" .)

I've seen this clue in The Globe and Mail.

Want a hint initially instead of a full solution? Install my app