"Magnum" is a term that is generally used for any cartridge of a perticular caliber that is capable of producing significantly great velocities by both burning more powder and creating higher pressures. The label serves both to differentiate the cartridge from its standard pressure cousins (7mm-08 Rem vs. 7mm Rem. Mag.), as well as a marketing tool to allow buyers to immediately distinguish the bigger cartridge. "Magnum" for rifle cartridges used to refer to only the belted cartridges similar to (and often based on) the .375 H&H. Today, the term "magnum" is used much more loosely and tacked onto just about any new cartridge the manufacturer want's to sell, even if the "magnum" doesn't significantly outperform the stardard pressure counterparts (the WSMs, except for the 270WSM, SAUMs, and WSSM's are examples of the the loose use of the term "magnum".) Then there are some true magnums that don't bear the magnum moniker, (i.e. the 7mm Shooting Times Westerner). As usual, there is no convention to this naming convention!

Mike