Copyediting is the level of editing that requires the least amount of editing work. These manuscripts are, for the most part, structurally sound with most content in the correct place. The manuscript is generally clear and easy to understand, but editing for grammar, punctuation, word usage, and spelling still needs to be done to make the manuscript ‘readable’ and acceptable for submission to peer review. These manuscripts may also need a small amount of editing to conform to journal requirements. Some commenting may be necessary to raise points with the author or to ask questions about unclear sentences. A majority (90%) of the manuscripts we edit are assessed at the copyedit level.

Engineering Sample Edit - TrackedCopy

Notes: The above excerpt is a “light” example of a Copyedit; some manuscripts need to be more heavily edited but are still at the copyedit level.
The following excerpt is from a “heavier” Copyedit manuscript:

Substantive Editing requires the most amount of editing work to bring the text to an English level acceptable for submission to peer review. Substantive level manuscripts need editing for grammar, structure, journal requirements, conciseness and general readability. Substantive manuscripts will have several comments regarding unclear sentences that will usually need to be further revised after the comments are responded to by the author. Only about 10% of manuscripts are so unclearly written that they require a full Substantive edit.
Comment from the above sample