In printing, the placement of images on both sides of a substrate.
The term duplex also refers to any substrate which possesses a different color or surface characteristic on each side, also referred to as duplex paper.
Duplex also refers to a laser (such as that used in a laser printer) that can image both sides of a sheet of paper at the same time.
In telecommunications, duplex refers to a system allowing an operator to simultaneously send and receive data, also referred to as full duplex, in contrast to half duplex, which describes a system whereby the user may send or receive data, but not at the same time. See also Simplex (second definition).