h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

...what's in this stuff. Hehe. Sorry, couldn't resist. I won't tell you, but someone else may wander by and say what it is if enough people get to wondering.

Incidentally, in addition to jelly being known in the US as Jell-O (a brand name which has essentially become generic even though it still exists, kind of like Hoover in the UK), jelly is the word here for another substance. I never liked it myself, but it's sweet, made of fruit or at least in fruit flavors and is a spread like jam (I think the word jam is universal, not sure, and I don't what exactly makes the distinction between one and the other, cos I don't eat the stuff). People spread it on toast or strangely enough (to me anyway) eat it on a sandwich with peanut butter.

First, JELL-O has indeed become a pretty generic way of referring to what non-Americans call jelly. Should you want to avoid any sort of copyright litigation, you should stick with the word gelatin. That works for the powder and the actual wiggly-jiggly stuff.
Second, though admittedly no expert on edible fruit pastes, I beleive the distinction between jam and jelly is that jam is thicker and is less likely to have actual bits of fruit in it. Jam is closer to a spread, while jelly is most easily classified as "goop." At the risk of sounding biased (literally: having two asses), I submit that jam is superior as a food product, because it's much easier to work with, and the flavor usually remains truer to the original fruit.
That's about all.

Never, NEVER put fuit in JELL-O. Ever. No good can come of it, trust me.

Does that include marshmallows?

Marshmallows should ALWAYS go in Jell-o. But never fruit. It's a smooth food, and people who put stuff like pineapple in there... I don't know.

I thought jelly was jam with the pips taken out. You know how rasberry jam or blackberry jam has pis in it, yes? Well jelly has them taken out. I think. Yes. That's it, no?