Other forms: haystacks
A haystack is a pile or bundle of hay. On farms, after hay has been cut, it's formed into haystacks until being fed to farm animals.
Haystacks come in different shapes and sizes, including piles of rectangular blocks of hay; rounded bales; and pointed piles of hay. These haystacks are all packed tightly, and they're often covered to protect them from the rain. You've probably heard the phrase "a needle in a haystack," an idiom that's used when a search is on for some impossibly tiny thing that's lost.