Rebirth is an ability utilize by Meta-Coolers in order to repair and upgrade themselves.
Once Meta-Cooler has been damaged, the Big Gete Star analyzes and repairs the Meta-Cooler unit, regenerating any lost body parts and upgrading them so that their armor will be more durable in order to avoid the same injury twice. However the Rebirth ability cannot repair a Meta-Cooler that has broken into pieces. Additionally, this ability has limits, as the combined onslaught of two Super Saiyans proved to be too much for Rebirth's armor increasing abilities to counter, and so it instead opted to create more Meta-Coolers to compensate. Even then, the full power of the two Super Saiyans proved to be too much for the Big Gete Star to handle, resulting in the destruction of the Meta-Cooler Corps. as each one exploded from the sheer amount of energy.