Trick used by artillerists to maximize the destruction of a bombardment.
Imagine a battery of howitzers, mobile rocket launchers, or mortars. In a conventional attack, when all the guns fire independently along the same approximate trajectory, the shells or rockets will arrive spread out over some time, giving the recipients time to spread out or take cover. In a time on target barrage, the guns will fire on different trajectories, first on long high arcs, then on medium trajectories, then low and fast. All the shells fired in this fashion will arrive more or less simultaneously. This allows even a small battery to wreak massive havoc, since the unlucky recipients of the fire have no warning and no time to escape. This type of barrage can, with excellent communications and control, also be spread between multiple batteries in different locations, causing even more destruction. Also, the (now-defunct) Crusader artillery system, with its robotic loading and powerful ballistics computers, was designed to be capable of launching a powerful time on target barrage using only one gun.
Update: Ouroboros informs me of the studies done by the US military on the psychological effects of this type of attack. Apparently the total artillery silence followed by the sudden bursting of huge numbers of shells devastates morale just as much as the physical destruction.