Copy editing, also known as line editing, is essentially the process of making each passage work. It will include grammatical corrections done inline as well as notes made for awkward sentences, word use recommendations, and other similar corrections. It will not address larger issues within the book as a whole. This is the most common form of editing I do. Structural and developmental editing focuses on content. This will include notes about pacing, tone, character development, continuity, and everything else that makes a book tick. This is necessarily somewhat subjective, but having an experienced editor give you unbiased feedback can be invaluable.