Sometimes you may find that your models are able to charge an enemy unit in the flank or rear. This is particularly good because an attack from an unexpected direction will sometimes throw the enemy into a panic and might give you an advantage in combat, too. A charging unit's position at the start of the Movement phase determines whether it charges into the flank, the rear or the front of the enemy unit.
If the charging unit is in the target's frontal zone when the charge is declared then it charges into the front. As units generally begin the game facing each other, this is the most common situation that will arise. However, if the charging unit comes from the flank zone, it charges into the side; if in the rear zone, it charges into the rear. See the diagrams below for more clarification.