Here is another personal favorite of mine (with which, I assure you, I am actually familiar). The description here is fairly straight forward – “the plot and story transpire during a distinct era in the past”. The period in which the author’s story is placed is generally essential to the narrative, such that the story would either not make sense or not make as great an impact if it were set during any other time. Now keep in mind, if you are thinking about writing in this genre, that the balance between fact and fiction is essential here. Your story and perhaps your characters are likely fictional (although some of my favorite examples of this genre have historical figures as some of their MCs), but the facts surrounding them have to be historically accurate to give your story legitimacy. (I can speak from experience: getting it wrong is embarrassing, at least.) This means research is essential and can be difficult. It’s not enough to have a play by play of the major Civil War battle during which you have set your story. You have to think of the other scenes in your story and get those details right as well. For instance, if your soldiers are having a heartfelt conversation over dinner about the loves they left at home, what are they eating? It’s unlikely to be a steak dinner with baked potatoes. (True, it’s unlikely that modern soldiers in battle are eating that either, but you get what I’m saying.) The amount of research that this takes to do well, can be daunting, so my best advice is to get to know your local university library very well, and maybe even make some connections with university professors whose research is related. If you are one of these professors, we should talk.