on Jane Friedman site:

Editors disagree about many of the finer points of their work such as whether to capitalize the word president (no, generally, but yes with President Lincoln), whether to spell out numbers (some styles say yes to every number lower than 10 or lower than 100), or whether to use the serial comma that preceded this clause (Chicago Manual of Style says yes). Some purists would argue that this post’s headline should read among instead of between. But I digress.

Editors also disagree about whether to start a sentence with And. And of course editors disagree about what constitutes the levels of editing that are often labeled copy editing, line editing, and proofreading—or just simply editing.

For guidance, I turned to the authority, the Chicago manual. Yet even that widely accepted all-knowing guide doesn’t make a distinction among editing levels: “Manuscript editing, also called copy editing or line editing, requires attention to every word and mark of punctuation in a manuscript, a thorough knowledge of the style to be followed, and the ability to make quick, logical, and defensible decisions.”

New authors are often confused about what level of editing they need, and rightly so. I hope to offer insight into the differences between line editing, copy editing, and proofreading.