In the bottom left are the various client computers accessing Second Life via the internet (the gray cloud I’m standing in.) In the back is the server farm that host the data of each of the "simulators" or "sims" of Second Life. The purple stuff in the very back are the different assets being delivered, including video, audio, images and other data.
Click on the image for more detail on what the various objects represent. Or visit the full model at this teleport link. Created by the Particle Lab.