Heavily planted??????

I would like to throw a somewhat philosophic question out to the group.  I have, over the last year or so, heard many references to having a heavily planted tank.  Mostly, these references refered to the fact that with a heavily planted tank you can eliminate algae through competitive inhibition of phospates.  I wondered what exactly the phrase "heavily planted" means.  Does this condition exist when you can no longer see the top of the substrate?  Is this a condition in which you have wall to wall plants?  I have a 150g planted tank with persistent algae issues, though improving slowly, and wondered just how many plants are neccessary to reach this illusive state of shangrala.

Scott Corbeil