Editing
An editor edits. However, there are many types of editors. A developmental editor will work with an author to create a book, organizing chapters, clarifying logic, and possibly fact-checking. A production editor works in-house, overseeing the production of books—press dates, copyeditors, indexers, proofreaders, binding—everything that needs to be done to make an author's manuscript become a printed book. A thorough overview of different types and levels of editing can be found on the Bay Area Editors' Forum.
An editor edits, and more specifically, a copyeditor copyedits. The simplest duties of a copyeditor include checking spelling, punctuation and grammar for correctness and consistency throughout a manuscript. Hyphenation, capitalization, and treatment of numbers and abbreviations are often a question of house style, and a copyeditor will ensure that these are applied consistently throughout the manuscript. A professional copyeditor will also pay attention to the audience and language of a manuscript: UK vs. US English and the grade level the work is written for are examples of audience awareness. A professional copyeditor is familiar with many style guides and will apply the appropriate rules to any given manuscript while not interfering with the voice of the author. Copyeditors may also be asked to do fact-checking or more substantive editing, including reorganization of some sections of the document. The scope of a copyeditor's work for any given project should be clearly delineated in advance, along with the appropriate fees.
A proofreader reads page proofs. Aside from the indexer, the proofreader is the last person to work on a book before it goes to press. It is the responsibility of the proofreader to correct any typographic, stylistic, or content-related mishaps which may have occurred as the book has been prepared. These may range from a simple misspelling to a difference between the table of contents and headings actually contained in the text. The proofreader may read the proofs against the copyedited manuscript, or may do a "cold reading," using only the proofs themselves.