This is the term for an office used among religious orders. In this context, the title is applied to a treasurer or financial officer of the group, with each level of the order having their own officer, from the local community (conventual) to that of "Procurator General", who supervises the finances for the entire order or religious congregation. Among the monastic orders, this title would be applied to the monk, normally residing in Rome, who was charged to act as an intermediary of the Order with the Holy See. In this he would represent the interests of the Order to the various papal offices which might have authority over the lives of the monks and nuns of that Order.
Like many terms used in the Catholic Church, this one comes from a similar title used during the Roman Empire.
An equivalent term in use among orders such as the Jesuits is "econome", which comes from the Greek.