What is "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.