Proofreading is the reading of a galley proof or an electronic copy of a publication to detect and correct production errors of text or art.
A proof is a typeset version of copy or a manuscript page. They often contain typos introduced through human error. Traditionally, a proofreader looks at an increment of text on the copy and then compares it to the corresponding typeset increment, and then marks any errors (sometimes called line edits) using standard proofreaders' marks. Unlike copy editing, proofreading's defining procedure is to work directly with two sets of information at the same time. Proofs are then returned to the typesetter or graphic artist for correction. Correction-cycle proofs will typically have one descriptive term, such as bounce, bump, or revise unique to the department or organization and used for clarity to the strict exclusion of any other. It is a common practice for all such corrections, no matter how slight, to be sent again to a proofreader to be checked and initialed, thus establishing the principle of higher responsibility for proofreaders as compared to their typesetters or artists.
Copy holding or copy reading employs two readers per proof. The first reads the text aloud literally as it appears, usually at a comparatively fast but uniform rate. The second reader follows along and marks any pertinent differences between what is read and what was typeset. This method is appropriate for large quantities of boilerplate text where it is assumed that the number of errors will be comparatively small.
Experienced copy holders employ various codes and verbal short-cuts that accompany their reading. The spoken word digits, for example, means that the numbers about to be read aren't words spelled out; and in a hole can mean that the upcoming segment of text is within parentheses. Bang means an exclamation point. A thump or screamer made with a finger on the table represents the initial cap, comma, period, or similar obvious attribute being read simultaneously. Thus the line of text: (He said the address was 1234 Central Blvd., and to hurry!) would be read aloud as: "in a hole [thump] he said the address was digits 1 2 3 4 [thump] central [thump] buluhvuhd [thump] comma and to hurry bang". Mutual understanding is the only guiding principle, so codes evolve as opportunity permits. In the above example, two thumps after buluhvuhd might be acceptable to proofreaders familiar with the text.