A hayride is a trip sitting in a cart or trailer filled with loose hay. It is not a way to move hay to the barn; it is a social outing that happens to use a hay wagon. In the United States people often go on hayrides in the autumn, at farms and festivals, sometimes at night, sometimes with a fire at the end. The hay is there to sit on, though actually it can be dusty and a bit scratchy. The word names the outing, not a special kind of car.