A prelature is the office of a prelate. Prelacy is the body of prelates as a whole, or a system of government, administration, or ministry by prelates.
In the Roman Catholic Church, the power to create Personal Prelatures was introduced in the Second Vatican Council; they are institutions having clergy and (possibly) lay members which would carry out specific pastoral activities. The adjective personal refers to the fact that, in contrast with previous canonical use for ecclesiastical institutions, the jurisdiction of the Prelate is not linked to a territory but over persons wherever they be.
The first Personal Prelature was Opus Dei, erected by Pope John Paul II in 1982.