After material has been copy-edited, the publisher sends it to a designer or typesetter. Their work is then displayed or printed, and that is the proof – proof that it is ready for publication. Proofreading is the quality check and tidy-up. However, some clients expect more than that.
Many proofreaders find they spot more errors on paper than on screen, but proofs may be read and marked in either medium. Proofreading is now often ‘blind’ – the proof is read on its own merits, without seeing the edited version.
A proofreader looks for consistency in usage and presentation, and accuracy in text, images and layout, but cannot be responsible for the author’s or copy editor’s work. The proofreader’s terms of reference should be agreed before work starts.