What is Chaplain?

Legal Definition
A chaplain is a non-denominational cleric (such as a minister, priest, pastor, rabbi, or imam), or a lay representative of a religious tradition, attached to a secular institution such as a hospital, prison, military unit, school, business, police department, fire department, university, or private chapel.

Though originally the word "chaplain" referred to representatives of the Christian faith, it is now also applied to people of other religions or philosophical traditions–such as the case of chaplains serving with military forces and an increasing number of chaplaincies at American universities. In recent times, many lay people have received professional training in chaplaincy and are now appointed as chaplains in schools, hospitals, companies, universities, prisons and elsewhere to work alongside, or instead of, official members of the clergy. The concepts of "multifaith", "secular", "generic" and/or "humanist" chaplaincy are also gaining increasing support, particularly within healthcare and educational settings.
-- Wikipedia
Legal Definition
A clergyman appointed to say prayers and perform divine service. Each house of congress usually appoints it own cbaplain.
-- Bouviers Law Dictionary
Legal Definition
An ecolesiastic who performs divine service in a chapel; but it more commonly means one who attends upon a king, prince or other person of quality, for the performance of clerical duties in a private chapel. 4 Coke, 90. A clergyman officially attached to a ship of war, to an army, (or regiment,) or to some public institution, fpr the purpose of performing divine service. Webster.
-- Black's Law Dictionary
Legal Definition
One officiating in a chapel.
-- Ballentine's Law Dictionary