SOG, sea-of-green. Basically, you can grow SOG with any number of plants if you're willing to train, bend or FIM stems. Or you can grow more and bud 'em out smaller without doing much of anything. Either way, what you're concentrating on is creating a solid canopy of tops at as uniform a level as possible.
SCROG, screen-of-green. Same as SOG, except uses mesh, netting or other horizontal support system. The goal is the same as SOG -- create a level, dense canopy -- but SCROG provides the grower with the opportunity to literally weave strains throughout the net or mesh.
Copied and pasted from another thread - I had trouble working it out too even when searching. I knew what sea of green was and assumed scrogging was teh same... but not quite!