Editing is certainly a part of it, but errors can also refer to continuity issues, or more commonly, historical inaccuracy. For a recent example, I was reading a book that was started by the author and finished by one of her friends after she had died. The original author was extremely attentive to historical details, with very minor changes as the plot necessitated. The new author didn’t have the same attention to detail; I remember her saying a character drank Jäegermeister as a small detail, in a historical setting a full twenty years before Jäger was invented. I don’t mind one or two of these errors, but the more they rack up the more I’m pulled away from the story. The more attentive an author is to accuracy and detail, the more likely I am to be impressed, even if the story isn’t necessarily something I would choose to read again 🙂