The term multiplex has its roots in the Latin words multi, which translates as many, and plex which translates as fold. So, a multiplexer folds, or interleaves, many transmissions onto a single circuit or channel. A typical multiplexer acts as both a concentrator and a contention device that enables multiple, relatively low speed terminal devices to share a single, high-capacity circuit between two points in a network. Multiplexers allow carriers and end users to take advantage of the economies of scale. Although the cost of the multiplexers and the high-bandwidth circuit that interconnects them involves additional cost, they can support a number of channels at a relatively low cost per channel.This approach is analogous to building a multi-lane superhighway. The cost of the high-speed highway is considerable, but the cost per lane and per vehicle mile is much more reasonable than the cost of building multiple single-lane, low-speed roads.There are a number of multiplexing techniques that can be employed, including Add/Drop Multiplexing (ADM), Frequency Division Multiplexing (FDM),Time Division Multiplexing (TDM), Statistical Time Division Multiplexing (STDM), and Wavelength Division Multiplexing (WDM). Inverse multiplexing performs the inverse process, spreading a high bandwidth signal across multiple lowerbandwidth circuits. See also ADM, FDM, inverse multiplexer, STDM, TDM, and WDM.