The whole term is "over bore capacity". As new slow powders are developed cartridges that were overbore aren't anymore. The .25-06 used to be overbore back when it was developed when the predecessors of 4064 and 4320 were considered slow. When 4350, 4831, and other slower burning powders came on the scene the .25-06 came into its own.
NOOB -- pronounced - New Bee; Noun; Someone who does not have a lot of experiance and is seeking advice; This is not a manufacturer of firearms rather an individual that is lacking knowledge.
Another label for cartridges is "balance". A "balanced" cartridge is one with a case capacity to bore size ratio which is efficient, meaning that bullet velocity is good considering the size of the powder charge. Increasing powder capacity results in higher velocities but each increase in powder capacity results in less velocity gain for the additional powder burned. An example would be the 7x57 Mauser compared to the 7mm Remington magnum or 7mm WSM. The 7x57 is more balanced, the magnums less balanced.