Desecrated Ground

From Dungeon Master's Guide, page 110.

Wilderness hazard

Some cemeteries and catacombs are imbued with the unseen traces of ancient evil. An area of desecrated ground can be any size, and a Detect Evil and Good spell cast within range reveals its presence.

Undead standing on desecrated ground have advantage on all saving throws.

A vial of holy water purifies a 10-foot-square area of desecrated ground when sprinkled on it, and a Hallow spell purifies desecrated ground within its area.