A Privileged Altar (Latin: Altare Privilegiatum) is an altar in a Roman Catholic church where a plenary indulgence is granted whenever Mass is celebrated there.
An example is the Vallarpadam Church in Kerala.
The term 'Privileged Altar' is used in the 1917 Code of Canon Law. The plenary indulgence is attached usually by the celebration of a Requiem Mass and benefits a soul in purgatory when Mass is offered for that intention at the Privileged Altar.
The grants of privileged altars were suppressed by Norm 20 of Pope Paul VI's Apostolic Constitution 'Indulgentiarum Doctrina'.
References
Privileged Altar Wikipedia(Text) CC BY-SA