The fluffy marshmallow gooey stuff that you get from the store.
Usually from the creators of the regular marshmallow unless you buy the great value kind like a cheap ass. It's really good, and can be easily addictive if you have too much if it.
Kid:"Hey mom! Did you get that fluff stuff from the store for our s-mores tonight yet?"
Mom: "Yes, I got it last night, dear"