There are other definitions available, but I just wanted to address some criticisms of the Twilight Saga.
It's a cliche vampire novel: No, not really. The author, Stephenie Meyer, never saw any vampire movies/read any vampire books. She admitted that she didn't really know the mythology, and so she made her vampires different because she focused on them as real people; hence, no fangs, garlic, wooden stakes, problems w/sunlight, etc.
It's poor literature: Really up to the individual reader in my opinion. Is it the most beautiful, perfect, polished writing? No. However, it is very descriptive and engaging, and the action parts are dramatic and exciting. Also, as even twi-haters have admitted, the books are addicting. That counts for something-the books are compelling to say the least.
Twilight fans are all idiot fangirls: Well, if you make sweeping generalizations about a group of people, then you are setting yourself up for comeuppance. That is just ignorant. If I said football fans are all thuggish muscle-bound jocks, is that the truth? Of course not. Don't judge the fans by a few that you've met, and don't judge the books just because everyone's talking about them.
Bella's and Edward's love is unrealistic/shallow/etc. : In Twilight, their love is portrayed as the out-of-this-world, destiny/fate, Romeo+Juliet kind. Not a lot of explanation, just an accepted fact. It's not realistic, but then it's not supposed to be. The story is about the complications that arise from their love. The love is not based entirely on looks/lust, but chemistry. It is idealized, perfect love. Just accept it.
The characters are stupid/dull/unrealistic: Again, matter of opinion. They are what they are. Personally, I don't like Bella, but I love Edward. Anyone who considers him shallow or pathetic should read the excerpt from Midnight Sun.
I just wanted to make this definition because I was distressed at the amount of prejudiced and negative comments about one of my favorite book series. Hopefully we can discuss it a little more civilly if everyone can just calm down and let people express their opinions.
None needed. If you want to criticize the Twilight books, read them first with an open mind.