i'm sure it has come to mean different things to different people... but if i were to say that i 'use the sea of green' method, to me it means that:
i have about one plant per sq. ft in the flowering chamber. I put one plant right next to another plant. (there are no holes or spaces to walk around really, i jam shite wall to wall as well if the light will reach that far.)
i try to grow clones rather than multipe seed stocks so that the plants stay about the same height. or, i at least bend and train plants to stay at the same height.
BTW, sea of green could be hydroponic or organic or whatever.
I top the plants at least once so that several 'kolas' form.
I try to have the plants finish at a height such that the bottoms of the plant are still receiving usefull amounts of light. (deffinitely 4 ft or less)