Hay

Hay was grass that had been cut, dried, stored, and was generally used for animal feed. Hay was sometimes stored in stacks, referred to as haystacks.

The Earth farmer kept several haystacks next to his silo on his farm in Broken Bow, Oklahoma. They were destroyed when the Klingon courier Klaang fired his disruptor at the silo in 2151. 

The idiom "needle in a haystack" referred to something being difficult to find or do. Miles O'Brien would occasionally use the term, as did Jadzia Dax once. 

Data and Artim played in haystacks on the planet Ba'ku before the USS Enterprise (NCC-1701-E) crew told Data it was time to leave.