One of the questions you have to ask yourself when you create the world of your fantasy or science fiction novel is how much of our world do you want to include in your world.
Science fiction set in our future is easy enough to figure out. Humans are humans whatever the time period. More than likely they will drink coffee or some form of caffeine beverage. Do you call it coffee or give it a new name?
Usually, the best answer is to just call it coffee if it’s in the background of the story because the reader has more than enough to keep up with otherwise. Generic terms like “shuttle” and “matter transfer machine” which are often used in science fiction can also be used.
Your created terms are best used for important elements of your world.
Fantasy is not as easy to figure out because, with the exception of some urban fantasy and contemporary fantasy, the world is built anew. Some choices are easy. A horse is a horse, a sword a sword.
Some common usages and terms, however, are jarring in fantasy. In the last week, I’ve read about a character eating a “hoagie” and “poppers,” and another using modern psychological terminology. Each time, the term knocked me right out of the story.
A writer really needs to think about the words she uses in relation to our world and the one created. Simple words like “sandwich” are jarring enough, but a term with a great deal of history behind it is a mistake every time.
We are always told to be specific in our language when we write, but, when we are creating a new world, going for the general term rather than the specific is often the best idea.