Any idea what the literature term of appearance is?

I got a book report coming up and it’s of comparing and contrasting two books that I recently read. I have to choose three things that I compare and contrast with (motivations, background, etc.). I’ve already decided the two in the parentheses but I need one more. And I chose appearance (external). Any idea what the literature term of that is? (it’s not for cheating, i wanna know what it means so i can choose it) If it’s what you look like, then I basically had no reason to ask this. :P