If a unit charges into combat and, by the end of that turn's combat all of its enemies have been wiped out, the unit may make a pursuit move, even with nobody left alive to pursue. This is an overrun move and represents the unit surging forwards, hungry to find more enemies to fight.
During this special pursuit move, victorious units move 2D6" or 3D6" directly forwards (as if they were pursuing a fleeing enemy to their front). Note that in this case the victorious unit does not have to pursue the player may always elect to automatically restrain pursuit if there are no fleeing enemies to pursue.