An altar server is a lay assistant to a member of the clergy during a Christian liturgy. An altar server attends to supporting tasks at the altar such as fetching and carrying, ringing the altar bell, helping bring up the gifts, and bringing up the liturgical books, among other things. If young, the server is commonly called an altar boy or altar girl. In some Christian denominations, altar servers are known as acolytes.

Clergy are formal leaders within established religions. Their roles and functions vary in different religious traditions, but usually involve presiding over specific rituals and teaching their religion's doctrines and practices. Some of the terms used for individual clergy are clergyman, clergywoman, clergyperson, churchman, cleric, ecclesiastic, and vicegerent while clerk in holy orders has a long history but is rarely used.