Relating to, having, or consisting of multiple elements or parts: "the whole complex and multiplex detail of the noble science of dinner\u201d ( Thomas Love Peacock). Relating to or being a system of simultaneous communication of two or more messages on the same wire or radio channel. A building, especially a movie theater or dwelling, with multiple separate units. To send messages or signals simultaneously using a multiplex system. To send simultaneously using a multiplex system.