"Just a friend"; a term often used to describe someone of romantic interest who has yet to be referred to as "
boyfriend" or "girlfriend" in public or even among close
friends. Often, both parties have a shared romantic interest in each other and haven't told anyone yet. At other times, one of them may be stuck in the friend zone. The "just a..." part is a lame attempt to conceal this
fact everyone else already knows. Otherwise, the term friend is used instead.