Non-fiction is factual, which means that it is presented as fact. The majority of the reading material with which we come into contact every day is likely to be non-fiction. What do a take-away menu and a scientific paper have in common? They are both non-fiction. The author's own opinions on the subject often come out in the form of bias, opinion, or emotive language, so the factual nature of what you are reading should always be questioned.