Michelle and I were discussing a post about this, and I'll probably do it when I get back from dropping off kids.

Every story can have definitions. If it is a magical story, it is often tied with the things that make our real world different from your story world. In a contemporary story, anything that requires research would be possible for definitions.

In Gone Girl, the author had to figure out how to do a lot of true crime things and explain them to us within the story. There's no magic, no speculative element, but I would bet there was research on whether a body could make it to the ocean from St Louis.