Pooks or stooks are the sheaves of hay before they're gathered up into one large hay mound or barn. They're usually 4 or more bundles of hay that have each been tied up into something that one person can get their arms around, or easily lift on a pitchfork.

I'm sure there's a Constable picture out there of a hay field dotted about with what looks like triangular stooks of hay or corn... they're waiting for the threshing machine or the hay wagon to come along, but they make cosy little nests for one or two people to be secluded if not actually private in. The danger in using the full sized haymound or stack, is that if it's badly made and you're extra vigourous, it could collapse on top of you.

LTS