"Oh... hm." How could he explain this? Normally he doesn't have to explain something like this since most people he talked to already knew about it. "Mana is like magical stamina, I guess would be the best way to put it. We tap into the Fade to cast spells, but it isn't like we can do it continuously, it requires us to expend energy. Depending on how big of a spell or how often you use them depletes this energy. It replenishes, but if you use more than what you're recovering it is possible to not be able to cast for a bit."