Fountain of Knowledge

The way I define either one is pretty straightforward, at least on the surface. The story has to deal with subjects that are interesting to/pertain to that age group, and have characters they can relate to.

I heard someone say (not here) "YA deals with more graphic issues than adult novels, like cutting and suicide and homosexuality"

But they see that because those are the topics they want to read about. I'm not saying those aren't intersting/of a concern to 'older' people, but they're more pertinent to a younger person's life and environment. Just like most (not all, don't even think I'm overgeneralizing here) teenagers aren't going to care about a book based in corporate america land. Unless its 'Big' or some simliar concept.

I do think things like graphic content level apply as well. It can't be too gorey/sexy/whatever. But to me that's not because the audience won't be interested, it's because by labelling a book 'YA' or 'MG' you're implying a certain content rating, similiar to a rating on a movie.

I agree with what Lorien is saying about talking like a kid, too. Slang is key. For instance, I struggle with words like: totes, yesh, nub, and epic. They're not a part of my normal vocabulary. I'd be more inclined to say totally, keen, sure, noob, or...okay, I do use epic, I lied. But you get the point. The rest of the verbiage might be the same, the conversational content might be the same, but the details are just enough different....