So from some fantasy books I've read, I've noticed that there are some authors who capitalize certain terms they have made up while there are others who never capitalize those made-up terms. For example, in Brent Weeks Nightangel trilogy, he never capitalizes the word "wetboy" which he uses to refer to an assassin that uses magic, and in David Dalglish's Dance of Cloaks, he never capitalizes the word "faceless" which he uses to refer to a religious group of assassins. But in Brandon Sanderson's Mistborn series, he capitalizes his magic users like Mistborn, Soothers, and Thugs. I also believe in Star Wars, terms like Jedi and Sith are always capitalized. I was wondering if there was a rule for this or is it just entirely up to the author?