A sabot is an exterior casing fitted around the exterior of a projectile in order to allow it to be fired from a larger diameter projectile weapon with a high degree of accuracy. In most cases the sabot is discarded from the main projectile once it has exited the barrel of the weapon.
In the case of armour piercing weapons the sabot is fitted to allow larger calibre weapons to fire projectiles that are thinner than their internal diameter at regular weapon speeds. In most cases the main projectile is long, thin and very hard/dense. This design results in a large force delivered at a focussed point very effectively, the use of sabots to fire thinner projectiles of equal mass at similar velocities has resulted in enhanced penetration and damage against hardened targets.