When an image is either printed out to check its quality, known as hard proofing; or when previewed on a monitor to simulate its final output, known as soft proofing.
Final comparison of a printed press sample with bluelines, artboards, original photographs, color mark-ups and other customer instructions to assure that the job is printing exactly as the customer intends.
Frequently used instead of "proving," denoting the operation of pulling proofs of plates for proofreading, revising, trail, approval of illustrations, and other purposes preliminary to production printing. In lithography, print proofs (photoprints) are used to check layout and imposition when plates are made from flats and colors.