Fragmentation is the process by which the casing of an artillery shell, bomb, grenade, etc. is shattered by the detonating high explosive (HE) filling. The correct technical terminology for these casing pieces is fragments (sometimes shortened to frags), although shards or splinters can be used for non-preformed fragments. The fragments can also be preformed and of various shapes (spheres, cubes, etc.) and sizes. Preformed fragments are normally held rigidly within some form of matrix or body until the HE filling is detonated. The resulting high velocity fragments produced by either method are the main lethal mechanisms of these weapons, rather than the heat or overpressure caused by detonation.