In the Roman Catholic Church, the term minister is used with various meanings. Most commonly, the word refers to a person, either lay or ordained, who is commissioned to perform some act on behalf of the Catholic Church. It is not a particular office or rank of clergy, as is the case in some other Christian organisations; rather, minister may be used as a collective term for vocational or professional pastoral leaders including clergy (bishops, deacons, priests) and non-clergy (theologians and lay ecclesial ministers). It is also used in reference to the canonical and liturgical administration of sacraments, as part of some offices, and with reference to the exercise of the lay apostolate.