There are several reasons for making proofs, not the least of which is to show the customer or client how the job was typeset and how the job will print. Proofs of text material are looked over by the typesetter and (in book publishing) proofreaders and the author, where typographical errors are flagged for later correction. At this stage, author alterations may also be indicated. The designer of the piece also examines the proofs to ensure that the type specifications have been enacted properly. All the corrections from the various copies of the proofs are then collated into one set of master proofs which is then sent back to the typesetter for correction. In book publishing, there are usually three sets of proofs: the first-pass pages, or the very first typeset pages; second-pass pages, or the pages with the corrections indicated on the first-pass pages having been made, plus final pagination. These second-pass pages are rarely sent to an author, and in-house and freelance proofreaders go over them again, looking for typographical errors. These proofs are followed by reproduction proofs (or repro for short) which are the camera-ready pages, gone over one last time for any egregious errors. Bluelines are also prepared prior to printing, as a means of checking the positioning of page elements, broken characters, and other non-content-related issues.
Color proofs are prepared photographically (see overlay color proofs or single-sheet color proofs) or digitally (see ["direct digital color proof [DDCP]"]) in order to show how the color separations have been made and how accurate they have been. Color proofs can also be made on press, preferably using the inks and substrate that will be used for the actual job. One set of these proofs constitutes the contract proof (or color OK), a color proof that is okayed by the customer and which serves as a master guide for the pressrun. A set of progressive proofs is also used to ensure that the colors conform precisely to the contract proof. (See Color Proofing.)
The term proofing also refers to the act of proofreading, or checking typed or typeset text for typographical errors or other mistakes.