There's some awfully big words there, Jonathan. But, sounds like pretty good answer.
To put it in a visual sense, If you were looking at a coral, or an anemone, and it was waving in the water, back and forth, little more than a soft wave, that would be a moderate flow. Not really blowing it around hard, just keeping it moving. You know, moderate!
Of course, if you are looking for a general answer about moderate overall flow in the tank, then forget what I said and go with the Bertoni answer.