It is basically the fat that collects on your back. fat rolls on your back, another physical signal of the fact that you are getting fat.
ask someone to pinch you in the back, if they manage to pull alot of skin then you probably have back meat.
Girl A: Hey, Shelly can you tie the back of my dress?
Girl B: (SHelly) : Sure, how tight?
Girl A: tight enough for it to hold, but not too tight, i dont want the back meat to show. I can hardly fit on this dress.