Every grouping for everything ever is arbitrary and has edge cases that don't neatly fit you dumb tranny.
Blobber does exactly that: it tells you how many characters a game has (more than 1) and how you move through its world (multiple characters moving as one).
It's a valid definition that's easy to understand.
So the only difference between Bioshock and Dungeon Master, is the number of characters. Otherwise Bioshock would be a blobber?
I'm trying to nail down this handy and easy to understand term.