It all depends on each person's interpretation. Intermediate being a point between two other points, based on a defined criteria.
You can have a wide range of power factors in one single caliber, example: .45 caliber, that spans from .45 ACP to .458 Win Mag. Somewhere there is an intermediate cartridge.
Then you can consider power factor only (energy) regardless of caliber, from .17 HMR caliber to .50 BMG....handgun to rifle, somewhere there is an intermediate cartridge.
The best case is a happy medium of all the above.