A reindeer is a large deer of the cold north, with long, wide antlers. In this species, females as well as males can grow them, which is not true of every kind of deer. They live in snowy places, in herds, and eat plants such as lichen. Some northern peoples keep them for milk, meat, and pulling sledges. Christmas stories give Santa a team of reindeer. Though actually, the written word looks like rein (the strap on a horse) plus deer, but that first half is not the horse word — it comes from an old northern name for this animal. In North America, wild ones are often called caribou; reindeer often means the ones people keep. Same family of animal, different habit of naming. The plural is usually reindeer, like sheep, not reindeers.