Ossuary is a Vampire Counts infrastructure building in Total War: Warhammer. Ossuaries are the resting places of skeletal remains, originally reserved for Morr's greatest subjects, but long since defiled.
Background
When a Priests of Morr perishes, his remains are treated with extreme reverence by his brethren and placed in a an ossuary, often located at the centre of a Garden of Morr. A Vampire Count that excavates such a find will be able to increase his Undead host quickly, as the remains are summoned to join them.