Case length
The length of the cartridge case alone, from the base to the mouth, not including the bullet.
Also called L3
One of the two length figures every cartridge entry carries, and the one that describes the chamber rather than the magazine. C.I.P. calls it L3.
It matters most where two cartridges share a bullet diameter and differ in case length, which is a deliberate safety arrangement rather than a coincidence. The .357 Magnum is a .38 Special lengthened by about three millimetres, and that extra length is exactly why a magnum will not chamber in a revolver built for the shorter round. The .44 Magnum and .44 Special work the same way.