When you shit on a girl's (or guy's I guess) chest. This the supposed pancake. And everyone likes their pancakes with syrup, so you jizz on the shit. The jizz is key, without it, you are performing a Cleveland Steamer. I'm not sure where the change from Cleveland to Boston takes place, but it's somewhere between the cum leaving the penis and landing on the shit.
My bitch forgot to clean up the Boston Pancake I made last night, but at least I didn't have to make my own breakfast.