Votive Mass
In the liturgy of the Roman Catholic Church, a votive Mass (Latin missa votiva) is a Mass offered for a votum, a special intention.
The Mass does not correspond to the Divine Office for the day on which it is celebrated. Every day in the year has appointed to it a series of canonical hours and (except Good Friday) a Mass corresponding, containing, for instance, the same Collect and the same Gospel. Normally the Mass corresponds to the Office, but on occasion, may not. These are votive Masses.
History
The principle of the votive Mass is older than its name. Almost at the very origin of the Western liturgies (with their principle of change according to the Calendar) Mass was occasionally offered, apparently with special prayers and lessons, for some particular intention, irrespective of the normal Office of the day. Among the miracles quoted by Augustine of Hippo in "De civ. Dei", XXII, 8, is the story of one Hesperius cured of an evil spirit by a private Mass said in his house with special prayers for him—a votive Mass for his cure.