A type of duplex copying that keeps the original document as an image in memory and not physically in a tray. Thus, rather than keeping a stack of one-sided copies until the copier is ready to copy on to the second sides, stackless duplexing allows you to make as many double-sided copies as you need, without being limited to the number of sheets a duplexing tray can hold at a time. Also referred to as trayless duplexing.