I have obviously not taken regional differences into account, here, and am shocked that people don't know what a Fluffernutter is! (Fluff is only available in 28 out of 50 states, and no other countries. This is probably why the rest of the world hates us.)
Fluffernutters are a delicious sandwich, made with peanut butter and creamy, marshmallow-y Fluff. If you go to that page, you can listen to the Fluff jingle, which clearly states that -
First you spread, spread, spread your bread with peanut butter
Add Marshmallow Fluff, and have a Fluffernutter.
When you enjoy, joy, joy your Fluff & peanut butter,
You're glad you have enough for another Fluffernutter.
And it's true, people. True!
Fluff is also very yummy in place of regular marshmallows on top of Hot Chocolate, in Harvard Squares, and useful when making fudge (although I have failed at the Never-Fail Fudge before, I'm ashamed to admit) or a quick frosting. It is made from "Corn syrup, sugar syrup, vanilla flavor, and egg white. There are no artificial preservatives, stabilizers, emulsifiers, or colorings in Marshmallow Fluff." It is similar to, yet different from (lighter and less meringue-ish), marshmallow creme.
Also good to know, but probably out of date: when my family visited Disney World in 1987 (20 years ago!), the Fluffernutter was served at the park, but was called a Donald Duck. PB & J was called the Minnie Mouse. So, for a while after that, in our house, Donald Ducks were the sandwich order of choice.
If I could, I would send you all some Fluff right now, because the fact that you have never had this sandwich makes me sad for you. If you are not lucky enough to live in a Fluff state, you can order some on this page (if you live in the lower 48, that is).