Larger and longer than a handgun cartridge, smaller than cannon cartridge/shell. It is a heavily nuanced distinction between a pistol and rifle cartridge that takes into account popular usage, designer intent, and various other factors.
A decent rule of thumb is that if the cartridge's length is more than 3.5 times the diameter of the case, it lacks a distinct rim, usually has bottlenecked case and the bullet diameter is approximately a half inch or less, then it is most likely a rifle cartridge regardless of specific calibre.