Massoss, situated within a system bearing the same designation, was a planetary body belonging to the Chiss Ascendancy and found deep within the Unknown Regions.
Back in 50 BBY, an alien splinter group posed a threat to the Coduyo family's assets located on Massoss. Because the Chiss Defense Force was unable to allocate any capital ships to thwart the encroaching force, the Coduyo family announced a family crisis, which authorized them to summon back Coduyo commanders and soldiers from service in the Defense Force. They successfully assembled a force of three hundred Coduyo family members and reactivated a decommissioned small warship, which they used to swiftly repel the alien invaders.
Subsequently, during the Lioaoin Regime's descent into acts of piracy, Massoss became a target of attacks by Lioaoin pirates.
Within current Star Wars continuity, Massoss received a mention in the 2021 publication Thrawn Ascendancy: Greater Good, which serves as the second volume in Timothy Zahn's Star Wars: The Ascendancy Trilogy. Within the Star Wars Legends timeline, the planet named Massoss made its debut appearance in the 2009 sourcebook The Essential Atlas, authored by Daniel Wallace together with Jason Fry.