A type of printing press, the web press prints on continuous rolls of paper or other substrates. Some web presses can print on both sides of the paper at the same time. It can consist of several connected units for printing different colors of ink and doing cutting, folding, and punching.
High-speed commercial web presses use wide rolls of paper for newspapers, books, etc. and use heat to set the ink (heat-set web). Small or cold-set web presses handle lower volume printing of forms, direct mail, and smaller publications with paper roll widths as little as 11 inches.
Newspaper presses can occupy several floors and contain multiple 4-color and single color printing units as well as a variety of folding sections to handle the different sections of the paper. The phrase Stop the presses! originally referred to stopping the running of these newspaper Web presses because of an extremely important late-breaking news story. If printing was already in progress but not too far along the papers in the press would likely be set aside or destroyed, the press reset, and a new version of the paper sent to the presses.