Discussion: What Makes Fiction Historical?

So I was sitting on the couch over the weekend reading Prisoner of Night and Fog and for some reason it triggered the thought in my brain, is this book considered Historical Fiction? So I of course bounce this off my husband as I always do.

Me: What do you think makes a book be considered Historical Fiction? If I read a book about the 80's (I'm thinking The Future of Us) is that considered historical?
Husband: Well then wouldn't a book you read that takes place yesterday be considered historical fiction?
Me: Hmm...does that mean everyone related to that era have to be dead before it's considered historical fiction?
Husband: I don't know.

So of course now I'm really thinking about this. I often think of it being eras where people wear skirts longer than their knees but then that's probably not right.

So what's the Webster's Dictionary Definition:
Historical fiction
Historical fiction is a literary genre in which the action that takes place in the past.

Well now that's totally broad. That could be a book that is referencing yesterday! I would really like to know what you think because I'm beyond curious.

What Makes Fiction Historical to you?