Copy edit

A copy edit is a correctness pass over a manuscript: grammar, punctuation, spelling, usage, consistency and basic factual continuity, applied against a chosen style guide and recorded on a style sheet.

A copy editor fixes subject-verb agreement, dangling modifiers, comma splices, hyphenation, capitalisation and number style. They enforce one spelling of every name from the first page to the last. They catch that your protagonist's eyes changed colour in chapter nine, that Tuesday became Thursday without a day passing, and that the pistol was a revolver two chapters ago. Anything ambiguous comes back as a query rather than a silent rewrite, because the voice is yours.

Fiction copy editing in the United States usually follows the Chicago Manual of Style with Merriam-Webster; British work more often uses New Hart's Rules with the Oxford dictionary. Every decision made along the way lands on a style sheet.

It sits after the line edit and before the proofread.

Two things it will not do: fix a structural problem, or make flat prose vivid. Those are a developmental edit and a line edit respectively, and no amount of correctness substitutes for either.