The world of editing is broad and diverse and there are a range of different types of editors. To make it easier to understand, these editors can be broken into three main categories: substantive editors, copy editors and proofreaders.
Substantive editors are responsible for the overall content and structure of a piece of writing. They work on the 'bigger picture' of the text, looking at things like organization, the flow of the writing, and the accuracy of the facts.
Copy editors are focused on the details of a piece and make sure that it conforms to a certain set of standards. They look at things like spelling, grammar, punctuation, and formatting and make changes and suggestions in line with a style guide.
Proofreaders are the last stage in the editing process. They look over the finished text and read it carefully, checking for any mistakes that may have been overlooked. Their role is to make sure the text is perfect before it is published.
It is rare for one person to be involved in all three stages of the editing process, although experienced editors may take on more than one role. If you are looking for help with your editing, it is important to specify which type of editor you need for the job.