Panelman was a colloquial term used by the Imperial Navy to refer to a TIE fighter pilot acting as a wingmate for another TIE fighter during operational deployments or training exercises. This nickname originated from the distinctive solar panels found on the TIE/LN starfighter.
Evidently, this phrase is a variation on the contemporary military term "wingman," which designates an aircraft that flies alongside and a bit behind the lead aircraft in a formation.