Virtual Power

Virtual Power (VPR) is similar to Minion Power except that it takes into account untrained experience. VPR is never shown directly, but is used internally by the game to prevent keeping a maxed Challenge Bonus by avoiding training (hence, increasing your Power); you'll have to keep finding different opponents as you earn more experience.

Gory details that you shouldn't care about: VPR is also used when calculating Max Tattoo and Clans Power allowances, and the purchase cost of Battle Allocation.