Altar server
An altar server, formerly called altar boy, is an assistant to a priest or minister during a religious service. Altar servers attend to supporting tasks at the altar such as fetching and carrying, ringing a bell etc. An altar server usually has no formal training and holds no formal religious position, i.e. is not a member of the clergy.
In the Roman Catholic Church, altar servers are usually young people. They carry the processional cross and candles; hold the book for the priest celebrant when he is not at the altar; carry the incense and censer; present the bread, wine, and water to the priest during the preparation of the gifts or assist him when he receives the gifts from the people; wash the hands of the priest; and assist the priest celebrant and the deacon as necessary.
One reason why the phrase altar boy has ceased to be standard is that recently girls have also serve in this capacity. In the Roman Catholic Church, altar servers that are studying to become priests or deacons might actually be acolytes, which is a necessary preparatory office before ordination. An acolyte may supervise children who are altar servers.
In Episcopal churches, all who serve in the above positions are called acolytes.