Stolen from a Hive chamber, what this tiny orb represents is unknowable and terrifying.
Used to upgrade weapons of Hive origin.
― In-game description

Embalming Orb was a legendary material added in The Dark Below. It was available to be purchased from Eris Morn. It was used to upgrade Husk of the Pit to Eidolon Ally.

In Update 2.0.0, the Embalming Orb was made no longer available for purchase and is no longer a requirement to upgrade Husk of the Pit.