it's a matter of being a class teacher vs one who only teaches a subject.
In East Africa, each primary and high school student belongs to a specific class with an assigned classroom for the entire school year; for high school you'll have the same classmates for all 4 years. Each classroom has a teacher that's in charge of it, and in most cases they will also be teaching a subject in that classroom. Each classroom will have multiple teachers, each teaching a different subject. However, not all subject teachers are in charge of classrooms, so not all teachers are class teachers