Holotank

Holotank is a device used to project to a hologram. The term is used to refer to both UNSC and Covenant devices.

UNSC
Holotanks are used to project a hologram of information and are sometimes reserved for AIs, though other information can be displayed, such as mission recordings and holo-vids. UNSC Holotanks vary greatly in size and shape, ranging from small cylindrical pedestals reserved for AI avatars to large tables used to display tactical information.

Covenant
The Covenant commonly use holotanks on their starships, and they are plentiful in High Charity as well. AIs can also access the map data from the holotank's link to the Covenant information network and give directions verbally to anyone near the holotank. In Halo 2, Cortana enters one to gain access to info in High Charity on the level Gravemind, remaining there for the rest of the game. The Covenant also utilize portable holotanks, referred to as Holo-Pedestals, to communicate over distance or in the battlefield.