It's just grass that has been cut, dried, and stored for later use as animal feed. While any type of grass can be used to make hay, certain types are better suited for it, like:
* Timothy grass: A common choice for horses.
* Alfalfa: A legume that's high in protein and energy.
* Orchard grass: A high-yielding grass that's good for various animals.
So, the next time you see a field of hay, remember that it's just regular grass that's been transformed into a nutritious food source for animals!