A druid was a priest in the old Celtic world, in places we now call Britain, Ireland, and France, before the Christian religion. Roman writers, including Julius Caesar in the first century B.C., talked about druids as people with high learning: they led holy rites, judged disputes, and were said to know the oak woods and the sky. We do not have books written by the druids themselves, so a lot of the picture comes from outsiders, and some of it may be tidier than the truth. People also use the word now for members of modern groups who try to follow old Celtic ways, and in games and stories for a nature-priest who can call on trees or change shape. Those later uses borrow the old name; they are not the same as the ancient priests.