A Battle Standard Bearer is a heroic model carrying a particularly impressive banner, and it will be presented as an option in your Warhammer army book. The battle standard is carried by a character model and, unless specified otherwise, the model that carries the battle standard cannot be the General.
Unlike normal standards, the battle standard is lost if the bearer is slain – other models cannot pick it up, even if they are in the same unit. As with other standard bearers, the battle standard bearer is automatically killed if he flees from combat – he dies on his feet, defending the precious standard to his last breath.