A chaplain is usually a religious leader — a minister, rabbi, or other clergy member — who works outside of a church or temple.
You can use the word chaplain to describe the minister who counsels patients at your local hospital. Or, a chaplain could also be a priest who lives and works with soldiers on a battlefield (a military chaplain). These days, many chaplains are non-denominational, not associated with any particular religion. The Latin root word, cappellanus, means "clergyman."