A Plenary Indulgence is granted to the Christian faithful who devoutly visit a cemetery and pray, even if only mentally for the dead from November 1st-8th (Octave of All Saints). The Plenary Indulgence can be gained on each on of these eight days. The indulgence is applicable only to the souls in Purgatory. On other days of the year this indulgence is a partial one.

The Handbook of Indulgences