In telecommunications and computer networks, multiplexing (sometimes contracted to muxing) is a method by which multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. For example, in telecommunications, several telephone calls may be carried using one wire. Multiplexing originated in telegraphy in the 1870s, and is now widely applied in communications. In telephony, George Owen Squier is credited with the development of telephone carrier multiplexing in 1910.

The multiplexed signal is transmitted over a communication channel, such as a cable. The multiplexing divides the capacity of the communication channel into several logical channels, one for each message signal or data stream to be transferred. A reverse process, known as demultiplexing, extracts the original channels on the receiver end.

A device that performs the multiplexing is called a multiplexer (MUX), and a device that performs the reverse process is called a demultiplexer (DEMUX or DMX).

A concurrency in a road network is an instance of one physical road bearing two or more different highway, motorway, or other route numbers. When two freeways share the same right-of-way, it is sometimes called a common section or commons. Other terminology for a concurrency includes overlap,coincidence,duplex (two concurrent routes), triplex (three concurrent routes) multiplex (any number of concurrent routes),dual routing or triple routing.

Concurrent numbering can become very common in countries that allow it. Where multiple routes must pass through a single mountain crossing, or through a major city, it is often economically and practically advantageous for them all to be accommodated on a single physical road. In some countries, however, concurrent numbering is avoided by posting only one route number on road signs; these routes disappear at the start of the concurrency and reappear when it ends. Criticism of concurrencies include environmental intrusion, as well as being considered a factor in road accidents.