Final part of the BEWBS scale. The "S" can stand for "Super".
These sizes are basically gag sizes to draw for fun based on a sequence or joke (or when drawing the waitress for "Juggalos" . I don't like to draw them that often usually because there's not much posing that can be done with these. Also, since the focus tends to be on the boobs, the face doesn't get as much attention, which is something of an issue with me since my opinion on a picture usually begins with the face (not to mention a pretty face makes boobs all the more enjoyable).
For those who don't get the meaning behind the "Juggalos" reference, please take a look at this: