What does when a girl says she missed you?

Well, it depends. If you were dating, but broke up, she might want to get back together with you. BUT THIS IS NOT ALWAYS THE CASE! Don't automatically assume that she still likes you. If you haven't talked in a while, she could simply miss talking with you. Especially if you are close friends. And of course she could simply want to see you again. It all depends on who it is, and what it's like between you. And never be afraid to ask questions, even if they seem stupid.