Developmental editing is for feedback on the major elements of your book, such as genre fit, story structure, characters, and plot. This type of feedback is largely subjective, so working with an expert editor who's familiar with your genre is critical. Example, "The ending scene needs more suspense."
Line editing involves feedback on how your book unfolds, covering pacing, plausibility, tone, and flow. It is mostly subjective, yet can be objective with the pointing out of factual inaccuracies. Examples, "This description of the forest should be shortened," and "The weather in this region in July would never be as cold as 50 degrees."
Copyediting gets you input on wording. It is a mixture of objective and subjective. Example, "Instead of using the word 'sprint' in this sentence, go with 'jog' or something similar." Proofreading involves finding issues with syntax, grammar, spelling, and punctuation. It is mostly objective feedback. Example, "Use the word 'hear' instead of 'here' in this instance."
Though copyediting and proofreading are different, since they both involve a word-level analysis, we discuss them as a pair, ie copyediting/proofreading.