I've been asked the difference between a line edit and a copy edit. Although the borders are blurry, editing takes place on three main levels. Globally, your editor will give you comments like, "His anger is never explained," or, "The book bogs down in the middle -- too much repeated information," or, "The ending's not dark enough -- you build toward a huge disaster but you don't deliver." That's the level (though not the actual comments) I've been working with my editor on for the last few months.

After that comes the line edit. This is your editor again, going through the book more closely, looking, as it were, at the trees, not the forest. At this level you get comments, written directly on the ms., like, "This guy has shrugged three times in this scene already. Find something else for him to do." Also at this level the editor will strike out extraneous (to her mind!) adverbs, etc., and point out to you that all your minor characters' names begin with the same letter.

Then comes the copy edit. This is not your editor, but a copy editor, whose job it is to check for syntax and grammar, facts, and internal consistency. The copy editor will point out that you said the car was almost out of gas but then the character drove around for two hours, and will also replace "was" with "were" in a condition contrary to fact. The copy editor will query a place where your character puts a dime in a parking meter, because in most places parking costs more than that, and will tell you that Jan. 3rd, 1978, wasn't a Saturday. Depending on the copy editor, you may also hear here that the guy shrugged three times already.