From Halopedia, the Halo wiki
The anti-gravity belt, sometimes shortened to anti-grav belt and also known as a gravitational mod belt, is a San'Shyuum gravity-mitigating mobility aid typically used when a San'Shyuum chooses to vacate their anti-gravity chair. It is worn around the waist underneath a San'Shyuum's robes. Rather than levitating its wearer like an anti-gravity chair, the belt merely reduces the gravitational pull the user is subjected to, allowing the San'Shyuum to walk more freely as they are a fairly feeble race. The belt's gravity-manipulation mechanism can also support its wearer during extreme acceleration of a spacecraft, for example, preventing them from being thrown about uncontrollably.
The Prophet of Stewardship was described as wearing an anti-gravity belt which he used to elevate himself above his subordinates in the original edition of Halo: The Flood; this is likely because the anti-gravity chairs had not yet been introduced into the canon at the time the novel was written despite being considered standard equipment for Prophets in later fiction. All mentions of Stewardship wearing a belt were replaced with "anti-gravity throne" in the 2010 reissue. Nevertheless, Halo: Broken Circle reestablished the anti-gravity belt as a canonical technology used in tandem with anti-gravity chairs.
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