They appear to be attempting to give it a distinct name here.
Rather than scattering when they come into contact with phonons, excitons in Re6Se8Cl2 actually bind with phonons to create new quasiparticles called acoustic exciton-polarons. Although polarons are found in many materials, those in Re6Se8Cl2 have a special property: they are capable of ballistic, or scatter-free, flow. This ballistic behavior could mean faster and more efficient devices one day.