From Halopedia, the Halo wiki
The DEMO variant of ODST armor bears resemblance to the late war design of the armor, with a notably more compact design. The front is equipped with a belt of grenades, and additionally comes equipped with a demolitions backpack. The armour's component pieces are capable of being employed on the Mark VI MJOLNIR platform. The ODST/DEMO armor is rated for vaccuum, allowing operators to perform short spacewalks on the exterior of spacecraft when needed.
Halo: Fireteam Raven
The ODST/DEMO armor is worn by players playing as Ava Lang. It confers no in-game effects.
As of Season 6: Raven, the ODST/DEMO will be available for use as an armor permutation in the Halo 3 component of Halo: The Master Chief Collection. Unlike the version seen in Fireteam Raven, this iteration comes equipped with a grenade belt. The base armor itself is directly taken from that used in the Fireteam Raven game rather than a recreation.
List of appearances