Not quite. It was merely a descriptor, a commonly used one.

The source of magic differs from world to world -- Generally, it is drawn from a certain substance that permeates certain worlds, known as mana. On occasion, the texts note that it really does flow in a 'stream' of sorts. Other times, however, mana may be drawn from within the body, or from artifacts, or from certain powerful creatures. I suspect that, due to the fusion of so many worlds, it would be most logical for the island to possess its own reservoir into which we tap.

. . . Was that intelligible enough?