Topic refers to the subject matter of a text.
Employers, teachers, and peers use a variety of terms that are synonymous to Topic: evidence, content, information, substance.
Our thoughts about topics are grounded in anecdotal experience, textual research, and empirical research. Topics have histories, genealogies, intellectual traditions. Discourse communities (AKA Communities of Practitioners) have developed intellectual traditions and research methodologies for discussing topics or conducting research on topics.
Different readers have different exposures to past scholarly conversations on a topic. And the rhetorical stances of readers and rhetors impinge on their openness to a topic, their willingness to view it critically and unemotionally.
Our rhetorical stances as rhetors–our experiences with families, schools, religions, cultures, ethnicities, gender–shape how we define, talk about, and research topics.