[1] Consumer and low-to-medium volume office printers use a duplexing unit that reverses a piece of paper after the first side has been printed.
Double-sided booklet formats (2:2 with a center fold) are also available, depending on optional outputs from the printer.
Long edge binding in portrait mode allows pages to be turned side-to-side like a book.
Short-edge binding allows the pages to be oriented correctly if they are flipped vertically, as in a notepad.
The turned sheet then continues its way through the press, being gripped at the opposite edge whilst the second side is printed.