A level above proofreading, light copyediting involves correcting obvious language errors and making relatively minor word changes to clarify and tighten the message. All other issues are met with queries.
Medium copyediting includes the same elements as above, but it calls for a bit more involvement, particularly in rewriting sentences for clarity and style. Issues that may have been queried under light editing will be subject to the editor’s judgement.
In heaving editing, matters of presentation and effectiveness come into focus. An editor might make significant rewrites to clarify the author’s ideas, helping the author to communicate in his own voice.
Substantive or Content
When you ask someone to help shape the text, you are calling for substantive editing. An editor will make decisions about content and organization, at your request. It may involve significant rewriting and can involve a higher level of collaboration.