The Orb of Osuvox is a Level 99 magic artifact that creates a spherical shield around itself that is completely impenetrable and indestructible to everything. The only way to activate or deactivate the shield is via a magic spell.
The Orb is used by IOI to shield Castle Anorak from outside gunter interference and ensure IOI's exclusive access to the Third Gate. Parzival manages to hack into IOI's data requisition system and detonate a bomb near the avatar using the Orb. The shield becomes deactivated, and in the ensuing chaos of the Battle of Castle Anorak, IOI loses the ability to reactivate the Orb.
The current location of the Orb is unknown; it was lost after the detonation of the Cataclyst.
A Level 99 Mage is required to keep both hands on the Orb to activate, and retain activation of, the Orb of Osuvox. So long as these conditions are met, an indestructible shield with a radius of half a kilometer will cloak the user and anything around him/her. The shield also penetrates the ground underneath the user, and encloses everything inside the shield.
While the shield is active, nothing can enter or exit the confines of the shield. This means that any player using the Orb would need to take precautions for long-term stays inside the shield until their task is complete. IOI brought varying degrees of weaponry and the majority of their army into the shield before engaging it. Additionally, as the avatar using the shield must keep both hands on the orb at all times, long-term usage of the shield would be limited by a player's need to eat, sleep, and bathe. IOI negated this issue by using a hacked rig that allowed passing control of the avatar in question to other people. Although this action was in violation of OASIS community guidelines, the hacked rig allowed multiple IOI personnel to control the same avatar and, thus, keep the Orb of Osuvox active indefinitely.
Of note, as the Orb of Osuvox requires a Level 99 Mage to activate, it seems the artifact would be non-functional in non-magic areas of the Oasis, although this has not been confirmed.